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I've been having a play around using em's/rem's today on a new site and have several things i'd like to discuss/ask on here.
For many years I have been totally a pixel based person with a few percentages thrown in when required.
I keep reading that em's and rem's are "the way" the web should be. Fair Enough which is why I gave it a go today.
So, first things first. Are the point of using em's/rem's for dimensions literally just for changing the dimensions of things relative to the main font size?
If so, then for what situation would you change the main font size? I have always set mine to be 16px and worked with it.
I located a Sass mixin that allows me to specify in pixels my dimensions for any property and it outputs it with rem and a pixel based fallback. I tweaked it to my liking first though.
So I then started building the site using the rem mixin for all my dimensions (margin, padding and a few heights). Yes everything scales when I alter the main font size but again, same question as number 2 here.
I used Compass Susy to set my grid up and used em's to specify it's settings, (I normally would have chosen pixels). I set the grid style within Susy to be the magic-grid which makes the grid static when the browser is wider than the grid but entirely flexible on the inside.
Surely everything that I have read about the benefits of using em's can be done using media queries? What do you guys do and most importantly what do the mainstream sites use?
Right, the next two questions are to do with images. I came across two situations today where using em's/rem's with an image somewhere in the equation resulted in a problem.
5a. I had an h2 set to inline block and added padding around and then the rem equivalent of 45px padding on the right. I set the line-height to a unitless value of 1.3. I then set an image to be the background of the h2 to appear over to the right to appear in the padding-right. At the standard base font size of 16px all is fine. However I increase or decrease that font size and the top and bottom of the image crop off. So question 2 again. I see why the image is getting cropped but it's how to deal with the relationship between em's/rem's and images that is bugging me.
5b. I had a div with a height set at the rem equivalent of 200px in height. I then added an image into there which had a height of 200px. The width of the image was set using the susy mixin span-columns to a specific column width and the height was set to auto. When the font size was altered I either ended up with an image too tall or too short. What is the best thing to do in this situation?
I was looking through some of the compass mixins available and for example this one:
#mixin pretty-bullets($bullet-icon, $width: image-width($bullet-icon), $height: image-height($bullet-icon), $line-height: 18px, $padding: 14px) {
margin-left: 0;
li {
padding-left: $padding;
background: image-url($bullet-icon) no-repeat ($padding - $width) / 2 ($line-height - $height) / 2;
list-style-type: none;
}
}
I can't add in all my em/rem stuff in there?
I think the over arching questions are:
Why are em's/rem's required in the first place?
How do you work with them in relation to images?
Any thoughts guys?
There is a lot to say about your post and it would probably be best to start with a few basics:
Why use em or rem units?
Em & rem units are used to size things relatively.
Em units: An em unit in a browser changes relative to it's parent's font-size, whether that is a span, p, div, body or html element. So when using em units for font sizes and for width or height, those dimensions will depend on the current parent's font-size.
Rem units: An rem unit in a browser is relative to the base font-size of the document. If you set that to 16px then 1rem is 16px, 2rem is 32px and so on. This means that you can change the scale of the entire document at a single point and anything that is using that relative measurement is going to increase/decrease accordingly.
The Point: These measurements are 'relative' so the answer to the question, "Why use em or rem units?", is for the em unit, simply use them when you want to size an element in a web page relative to it's parent and for the rem, use them when you want to size an element relative to the document.
That's a simple approach but it puts web design in the right context for the next question...
How should em & rem units be used in design and layout?
The answer to this question is also multifaceted but to put it in simple terms using em, rem or any 'relative' measurement to describe elements in your design is a move away from static pixel based design.
For the most part em, rem & percentages are used for creating flexible layouts and flexible layouts have a whole different approach to the web and using elements within them than pixel based design. For instance, if you have a container that needs to expand relative to the document width and it has an image in it, you'll probably want that image to resize along with the container or situate itself differently depending on the available space.
Here's where we get into 'Responsive' designs and layouts in an attempt to make 'Adaptive' sites & applications and also where Media Queries and other techniques come in.
Personally I use em's almost exclusively for type and margins & padding of elements. Dimensions I describe in percentages and then it's almost always only the widths. There's only so much you can control in a world where the devices, device dimensions and pixel ratios keep doubling every year.
So to sum up, sort of...
1) If you need static dimensions just stick with pixels. There is generally no real benefit to using relative measurements if you need specific fixed dimensions.
2) Em's & rem's are one of many tools and serve their purpose as other tools (pixels) serve theirs. They are a great tool and worth mastering so use them when you need to but only when the problem requires relative sizing.
3) You may want to split those Compass Susy questions into a more specific post and provide some example if you want help with that.
I hope that helps even if it doesn't answer all of the questions you have here.
Cheers
Ems/rems are used to make the site adaptive to different settings on the client end. My browser settings can increase or decrease the font size on your site, and using em/rem allows you to adapt to my settings. It's a trade off - as with everything else in web design - between your pixel-exact control and your willingness to design around change and user control. There is no right answer - but I like to remind myself that the entire technology of the web is weighted towards user control, and any attempt for me to be pixel-anal is fighting against the core technologies.
Ems/rems can be used in media-queries to set breakpoint widths, but they solve a different part of the adaptability formula - font size, rather than screen size. Your Susy grid can now adapt to both at once!
Images are a pain for any kind of responsive/adaptive design work. The same solutions you might use for a fluid layout will help with an em-based layout. Common solutions involve the background-size property (Compass has a mixin for it) and setting html images to a max-width of 100%. See CSS-Tricks Rundown of Handling Flexible Media. I have use this fluid-media mixin to handle the "intrinsic ratios" approach for background images and the like.
But, more often than not, I find a way to design with fewer images. I like that the technology pushes me towards simplicity in that area - so it doesn't bother me.
I'm redesigning my site because looks awful on different resolutions (apart devices), most guides and tutorials rely on % and em than fixed values. I'm still learning this so I'm reading everything around.
Thought this would solve the question with different display sizes but again: we have to craft some more CSS for fix some specific issues.
If I need to add media-queries for extra display sizes, why use % then? Do use % really reduce coding? Is ok need to add some extra css for some sizes or am I doing something wrong?
Thanks for any advice!
The purpose of using em sizes is to allow the base your design off of the user's choice of font size. I may use a larger font size because I have a huge monitor and poor eye sight, while someone else might prefer a smaller font. By using em units, your design will accommodate both of our font preferences and resize accordingly instead of forcing the font size to a given standard (eg. "12 point font").
In a similar manner, percent (%) units allow your design to respond to different browser sizes. Used in conjunction with em units, this will allow text-based elements to respond to arbitrary font size choices, and layout elements to respond to arbitrary browser sizes.
It is perfectly acceptable to design a single responsive design for all media types. Media queries are intended when you want different display styles on different devices, not to "support" different display sizes. An example would be to use serif fonts on print media and sans-serif fonts on display media, since usabilities studies have shown that these font faces are preferred for these sorts of media.
Furthermore, it allows you to do custom styling for some situations like mobile devices, where you may want to consider that the user has a limited amount of bandwidth and maybe cut down on extra images. Or if you want to display your content in a completely different layout for the microscopic screen afforded by certain phones.
% allows your site to be responsive to the user's method of viewing. Let's say you have a div that's at 100%. It'll fill the entire section, regardless if it's on a phone or desktop.
It should be okay to add extra CSS for sizes as well. As far as I know, you can have some elements display in % and some with a fixed px value, although they might conflict depending on how the page is setup or what it is being viewed with.
For example.
Your website header have the width of 950px; But in a mobile device, it may fit at 450px;
So, you use media-query to reposition some elements and handle some size issues and set the header width to 450px;
But, if you use % values, you can set your header div to have 100% of width base in its parent. So you can only change the body or some container div width, the all childs going to adapt.
Diana,
I am glad I came across this question. I literally just uploaded my first responsive design which is 90% based off of percentages when it comes to font-size and widths.
Check out the below:
http://www.noxinnovations.com/portfolio/responsive/
Obviously, it doesn't look amazing, and the image looks way out of place... But do me a favor and resize your browser window, by slowly making it smaller and smaller. I did that by setting a percentage width!
Trust me, I tried doing this responsive design test with pixels, and it didn't turn out too well. The percentage width ensures that regardless of the resolution and or pixel dimensions (per se) the design will always cater to the size of the screen. Also, I did not have to use one CSS3 Media Query, but I would highly suggest using CSS3 Media Queries only when you need them.
In my opinion, I should probably have a Media Query for a larger screen.
I hope this helps you as much as it has helped me!
Thank you,
Aaron
What is the difference between pt and px in CSS? Which one should I use and why?
px ≠ Pixels
All of these answers seem to be incorrect. Contrary to intuition, in CSS the px is not pixels. At least, not in the simple physical sense.
Read this article from the W3C, EM, PX, PT, CM, IN…, about how px is a "magical" unit invented for CSS. The meaning of px varies by hardware and resolution. (That article is fresh, last updated 2014-10.)
My own way of thinking about it: 1 px is the size of a thin line intended by a designer to be barely visible.
To quote that article:
The px unit is the magic unit of CSS. It is not related to the current font and also not related to the absolute units. The px unit is defined to be small but visible, and such that a horizontal 1px wide line can be displayed with sharp edges (no anti-aliasing). What is sharp, small and visible depends on the device and the way it is used: do you hold it close to your eyes, like a mobile phone, at arms length, like a computer monitor, or somewhere in between, like a book? The px is thus not defined as a constant length, but as something that depends on the type of device and its typical use.
To get an idea of the appearance of a px, imagine a CRT computer monitor from the 1990s: the smallest dot it can display measures about 1/100th of an inch (0.25mm) or a little more. The px unit got its name from those screen pixels.
Nowadays there are devices that could in principle display smaller sharp dots (although you might need a magnifier to see them). But documents from the last century that used px in CSS still look the same, no matter what the device. Printers, especially, can display sharp lines with much smaller details than 1px, but even on printers, a 1px line looks very much the same as it would look on a computer monitor. Devices change, but the px always has the same visual appearance.
That article gives some guidance about using pt vs px vs em, to answer this Question.
Here you've got a very detailed explanation of their differences
http://kyleschaeffer.com/development/css-font-size-em-vs-px-vs-pt-vs/
The jist of it (from source)
Pixels are fixed-size units that are used in screen media (i.e. to be read on the computer screen). Pixel stands for "picture element" and as you know, one pixel is one little "square" on your screen.
Points are traditionally used in print media (anything that is to be printed on paper, etc.). One point is equal to 1/72 of an inch. Points are much like pixels, in that they are fixed-size units and cannot scale in size.
Have a look at this excellent article at CSS-Tricks:
px – em – % – pt – keyword
Taken from the article:
pt
The final unit of measurement that it is possible to declare font sizes in is point values (pt). Point values are only for print CSS! A point is a unit of measurement used for real-life ink-on-paper typography. 72pts = one inch. One inch = one real-life inch like-on-a-ruler. Not an inch on a screen, which is totally arbitrary based on resolution.
Just like how pixels are dead-accurate on monitors for font-sizing, point sizes are dead-accurate on paper. For the best cross-browser and cross-platform results while printing pages, set up a print stylesheet and size all fonts with point sizes.
For good measure, the reason we don't use point sizes for screen display (other than it being absurd), is that the cross-browser results are drastically different:
px
If you need fine-grained control, sizing fonts in pixel values (px) is an excellent choice (it's my favorite). On a computer screen, it doesn't get any more accurate than a single pixel. With sizing fonts in pixels, you are literally telling browsers to render the letters exactly that number of pixels in height:
Windows, Mac, aliased, anti-aliased, cross-browsers, doesn't matter, a font set at 14px will be 14px tall. But that isn't to say there won't still be some variation. In a quick test below, the results were slightly more consistent than with keywords but not identical:
Due to the nature of pixel values, they do not cascade. If a parent element has an 18px pixel size and the child is 16px, the child will be 16px. However, font-sizing settings can be using in combination. For example, if the parent was set to 16px and the child was set to larger, the child would indeed come out larger than the parent. A quick test showed me this:
"Larger" bumped the 16px of the parent into 20px, a 25% increase.
Pixels have gotten a bad wrap in the past for accessibility and usability concerns. In IE 6 and below, font-sizes set in pixels cannot be resized by the user. That means that us hip young healthy designers can set type in 12px and read it on the screen just fine, but when folks a little longer in the tooth go to bump up the size so they can read it, they are unable to. This is really IE 6's fault, not ours, but we gots what we gots and we have to deal with it.
Setting font-size in pixels is the most accurate (and I find the most satisfying) method, but do take into consideration the number of visitors still using IE 6 on your site and their accessibility needs. We are right on the bleeding edge of not needing to care about this anymore.
A pt is 1/72th of an inch and is a useless measure for anything that is rendered on a device which doesn't calculate the DPI correctly. This makes it a reasonable choice for printing and a dreadful choice for use on screen.
A px is a pixel, which will map on to a screen pixel in most cases.
CSS provides a bunch of other units, and which one you should choose depends on what you are setting the size of.
A pixel is great if you need to size something to match an image, or if you want a thin border.
Percentages are great for font sizes as, if you use them consistently, you get font sizes proportional to the user's preference.
Ems are great when you want an element to size itself based on the font size (so a paragraph might get wider if the font size is larger)
… and so on.
pt is a derivation (abbreviation) of "point" which historically was used in print type faces where the size was commonly "measured" in "points" where 1 point has an approximate measurement of 1/72 of an inch, and thus a 72 point font would be 1 inch in size.
EDIT: Note to clarify
There are approximately 72 (72.272) points in one inch or 2.54 cm. The point was first established by the Milanese typographer, Francesco Torniella da Novara ( c. 1490 – 1589) in his 1517 alphabet, L'Alfabeto. (you can search for various references to those)
px is an abbreviation for "pixel" which is a simple "dot" on either a screen or a dot matrix printer or other printer or device which renders in a dot fashion - as opposed to old typewriters which had a fixed size, solid striker which left an imprint of the character by pressing on a ribbon, thus leaving an image of a fixed size.
Closely related to point are the terms "uppercase" and "lowercase" which historically had to do with the selection of the fixed typographical characters where the "capital" characters where placed in a box (case) above the non-capitalized characters which were place in a box below, and thus the "lower" case.
There were different boxes (cases) for different typographical fonts and sizes, but still and "upper" and "lower" case for each of those.
Another term is the "pica" which is a measure of one character in the font, thus a pica is 1/6 of an inch or 12 point units of measure (12/72) of measure.
Strickly speaking the measurement is on computers 4.233mm or 0.166in whereas the old point (American) is 1/72.27 of an inch and French is 4.512mm (0.177in.). Thus my statement of "approximate" regarding the measurements.
Further, typewriters as used in offices, had either and "Elite" or a "Pica" size where the size was 10 and 12 characters per inch respectively.
Additionally, the "point", prior to standardization was based on the metal typographers "foot" size, the size of the basic footprint of one character, and varied somewhat in size.
Note that a typographical "foot" was originally from a deceased printers actual foot. A typographic foot contains 72 picas or 864 points.
As to CSS use, I prefer to use EM rather than px or pt, thus gaining the advantage of scaling without loss of relative location and size.
EDIT: Just for completeness you can think of EM (em) as an element of measure of one font height, thus 1em for a 12pt font would be the height of that font and 2em would be twice that height. Note that for a 12px font, 2em is 24 pixels. SO 10px is typically 0.63em of a standard font as "most" browsers base on 16px = 1em as a standard font size.
Yes, "px" means "pixel"
Now that I said it, I can already hear an army of clairvoyants approaching, with "px has nothing to do with pixels" on their banners. They're so proud of knowing better that they look up every comment containing the original truth and explain in detail that it's false, incorrect, misleading, etc.
And yes they have a point - a very specific point in time, actually, called iPhone 4.
Here's what happened.
The peaceful days
Before Retina displays, one pixel was one pixel. Because that's how it should be, according to human logic. You put a single pixel line on the screen, you magnify the hell out of it, and there you go: it's exactly ONE PIXEL wide. On many hardwares, modern ones included, this is still the case, so it's everything but "incorrect" to say 1px = 1 pixel.
But.
Back then, one day, iPhone 3 was followed by iPhone 4, doubling the resolution in both X and Y, and the developers of Safari worried that all webpages will look ricidulous, especially because many web developers relied on the steady 320x480 resolution. So just creating a 640x960 pixel area would have killed most of the sites. And at this point, someone had the billion-dollar idea to introduce a magical beast: a CSS feature called -webkit-min-device-pixel-ratio - on iPhone 3 it was 1, and on iPhone 4 it was set to 2 by default. Meaning "1 CSS pixel now means 2 screen pixels". A very ugly hack to keep websites look somewhat intact - it worked at that time, with the very small cost of some images looking a bit blurry, but in the long run it caused this worldwide misunderstanding of poor old px who actually did nothing wrong.
So then: pt or px?
On screens, use px because on many-many displays it will mean ONE PIXEL. The biggest advantage of using pixels is they look crispy; even if 1px means 2 or 3 physical picture elements, whatever you draw will start at the boundary, not somewhere-in-between. This is very important. Watch any browser animation that includes text, especially size transitions: when you increase a div to double size, but slowly. You'll see how your browser recalculates its pixels and redraws the font when the animation is done. There's a temporary image of the area which is a little blurry - to make the animation itself smoother -, and then, after reaching its final state, a more exact image is calculated. See this CodePen.
1px is always an integer multiplication of hardware pixels; that is, unless your operating system is being smart like resizing your whole desktop to sqrt(2) x PI. Or just 125%, yes, hello Windows on tiny laptops. But anyway - with px, you have the highest chance to align your things with the physical grid.
What about pt? The funny thing about pt is it's actually translated to px, so it's just a worse way to specify pixel sizes. Here's a calculator. Points (since they come from the print world) start to make sense when you print something, but today there are better alternatives, depending on what you need - so tbh, points are almost never needed.
TL;DR
For screens, use px whenever possible.
I read somewhere on a site :
In principle, using a px measurement for font-size is not a good idea. A handful of browsers will prevent the font from being resized by the user if you do this.
Is this right??
Is this right??
Well, yes, certainly there are a few (generally older) browsers that won't let you resize the text when it's sized in px, pt, in, mm and so on.
But even in browsers with a working zoom, it's polite to work relative to the user's stated preference for font size, so they don't have to resize the text or zoom the page manually to make it comfortable. (Fixed fonts plus fixed width page can be particularly bad for this in page-zooming browsers as zooming up is likely to make the columns of text too wide to fit the screen.)
In principle, using a px measurement for font-size is not a good idea.
I wouldn't go so far as to say it's always a bad idea.
There are often elements on the page where you want the text to be sized to match an image (say, a header with text below it that should fit more-or-less without wrapping, or text above a background image made to fit it). In that case you should use px to make fonts and images line up nicely.
For the page's main body text, yes, it's nicer to use em/% and let the user decide the size. But for text that plays a part in the page's graphical layout, px fonts are typically the best bet.
The issue is mainly with aspect ratio. Let's say my resolution is 1024x768 for an aspect ratio of 1.33. For 1920x1080, the aspect ratio becomes 1.77, meaning that any image displayed at a specific pixel width and height will be a different size in inches due to the scaling effect of the aspect ratio. The same basic issue exists if you zoom as you are effectively using the aspect ratio in the zoom window.
Most websites get around this by using em which, to be honest, suffers from some of the same downfalls as any other rendering mode. Even "device independent pixels" are based on the DPI of a monitor. So, use em knowing that it just has less faults than px, not because it's perfect.
Read the following article if you want a more in depth study.
http://www.w3.org/WAI/GL/css2em.htm
Yes, at least IE6 & IE7 do that. Take a look at How to Size Text in CSS.
Quoting CSS: The Definitive Guide by Eric Meyer
There is one more value that is
potentially the same as 36pt, and
that's 36px, which would be the same
physical distance if the display
medium is 72 pixels-per-inch (ppi).
However, there are very few monitors
with that setting anymore. Most are
much higher, in the range of 96ppi to
120ppi. Many very old Macintosh web
browsers treat points and pixels as
though they are equivalent, so the
values 14pt and 14px may look the same
on them. This is not, however, the
case for Windows and other platforms,
including Mac OS X, which is one of
the primary reasons why points can be
a very difficult measurement to use in
document design.
Because of these variations between
operating systems, many authors choose
to use pixel values for font sizes.
This approach is especially attractive
when mixing text and images on a web
page, since text can (in theory) be
set to the same height as graphic
elements on the page by declaring
font-size: 11px; or something similar,
as illustrated by Figure 5-15.
Using pixel measurements for font-size
is certainly one way to get
"consistent" results with font-size
(and, indeed, with any length at all),
but there is a major drawback.
Internet Explorer for Windows up
through Version 6.0 does not allow
users to easily resize text that has
been set with pixels. Other browsers,
including Mozilla, Netscape 6+,
IE5+/Mac, Opera, and even IE7, allow
the user to resize text no matter how
it's been set. Thus, using pixels to
size text is no more of a guarantee
that it will stay the same size than
is any other method. The other
approaches discussed in this chapter,
such as keywords and percentages, are
a much more robust (and user-friendly)
way to go, as they can be used to
scale text from the user's default
font size.
That said, the issue here is what unit to use for your body element. In most cases, you should use the em unit for other elements like headings and paragraphs.
what are cons to use relative values em and % for fonts, What is rounding problem? and how to avoid/solve rounding problem. Is there any calculator?
How to use relative values as easy as we use px
There are not a lot of cons using em or %.
Sometimes i had trouble to make fonts look exactly the same size in IE and the normal browsers. But most of the time i have to do a IE CSS anyway so its not really a problem.
When you define fonts in PX, the fonts are not antialiased on some computers running windows. If you use EM or % they are and you have a very precise control of the font size. (1.249em for example).
Unlike #scunliffe i would always use EM as font-size. Even when you have fixed design withs. Sometimes its not possible to do a pixelperfect design with PX fonts, because fonts rendered by Photoshop looks different then in the browser.
I have made a test tool to show the differences:
http://bluesys.ch/csstest/
and here you can find a tool to convert your PX values in to EM:
http://pxtoem.com/
I may be preaching to the choir here, but I find the Firefox "Web Developer" addon is a real help when I'm dealing with font sizing.
https://addons.mozilla.org/en-US/firefox/addon/60/
Use 'Information' > 'Display element information' to view the exact pixel size for your (relatively sized) element. Tweaking the CSS (to within 1 decimal point) until the amount returned is a round number minimises the chances of your text being different sizes in different browsers / operating systems.
Oh, and from my current project:
Standard (appearing as 12px) font set on site wrapper is 75% (body is 100%) , then use:
14px: 116.7%
16px: 133.3%
18px: 150%
18px: 166.7%
There are loads of reasons to not use fixed text sizes (accessibility being the big one), and once you've spent a while getting your CSS sorted you'll never look back.
Here's a nice little trick for you.
In the your CSS, set the font-size on the BODY of the document to 62.5%.
Now, whenever you want to set a font-size, you use EM values. 1.1em would be equivelant to 11px and 1.2em to 12px and so on.
That's how I work anyhow.
Good luck.
Michael.
I don't believe there are (m)any cons. Using px limits your ability to scale text in IE6 but otherwise using % or em should allow you to scale nicely.
The only con I can think of is that if you want your text to be exactly 12pt, or 13px then using % or em isn't what you want. However If you are trying to create a fixed width design where everything is measured out to the pixel I would advise against it. The Web is a free-flowing canvas... each user has a different sized window, personal font/zoom size choice and Operating System differences. Your content should look good on any screen by adapting to the real-estate you are provided with.
em vs px is like a holy war. Everyone has their own ideas on what's best. Using px is perfectly fine, the only real problem is that text will not resize in IE6.
One other issue is how much you will change your mind about the general font size. If you do everything in absolute values (px, pt), then decide the font size across the site is too small, then you might have to change a lot of values to make everything bigger. Conversely, if you do everything in relative values (em, %) then you want to change the size of one thing only, it will affect all its child elements.
In the end, the best choice is to simply be consistent.