figure out how many circular frames fit on screen xamarin.forms - xamarin.forms

Question

I want to create a grid with circular frames according to the number of students in a class. i want to display them i a way that the number of frames in each column fit the screen and i'll have rows added accordingly, so i tried to do something like this as a trial:
xaml:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="stdprofiles.MainPage">
<StackLayout Orientation="Horizontal" >
<Grid x:Name="thislayout" HorizontalOptions="Center" Margin="20,20" >
</Grid>
</StackLayout>
</ContentPage>
xaml.cs:
public MainPage()
{
InitializeComponent();
var width = DeviceDisplay.MainDisplayInfo.Width;
var height = DeviceDisplay.MainDisplayInfo.Height;
double nbofcolumns = width / 150;
double nbofrows = 10 / nbofcolumns;
double ans = nbofcolumns * nbofrows;
for (int i = 0; i < nbofcolumns-1; i++)
{
thislayout.ColumnDefinitions.Add(new ColumnDefinition { Width = 100 });
}
for (int j=0;j< nbofrows+1; j++)
{
thislayout.RowDefinitions.Add(new RowDefinition { Height = 100 });
}
for(int i=0;i<10;i++)
{
SwipeItem delete = new SwipeItem
{
IconImageSource="deleteic.png",
BackgroundColor = Color.Transparent
};
List<SwipeItem> swipeItems = new List<SwipeItem>() { delete };
Frame circleImageFrame = new Frame
{
ClassId=i.ToString(),
Margin = 10,
BorderColor = Color.Black,
CornerRadius = 50,
HeightRequest = 100,
WidthRequest = 100,
IsClippedToBounds = true,
HorizontalOptions = LayoutOptions.Center,
VerticalOptions = LayoutOptions.Center,
Content = new Image
{
Source = ImageSource.FromFile("user_profile.png"),
Aspect = Aspect.AspectFill,
Margin = -20,
HeightRequest = 100,
WidthRequest = 100
}
};
SwipeView swipe = new SwipeView
{
TopItems = new SwipeItems(swipeItems),
Content=circleImageFrame
};
thislayout.Children.Add(swipe, i%(int)nbofcolumns, i/(int)nbofcolumns);
delete.Invoked += delegate
{
thislayout.Children.Remove(swipe);
};
}
}
the point is that i got the width of my phone screen then divided it by 150 because i specified that i want my column's width to be 100. the thing is that it's not working, the number of columns obtained do not fit the screen like i got 7 columns and only 4 columns fit the rest do not appear and so i didn't get correct number of rows. another thing surprised me is that when i tried displaying the width obtained I got 1080 (for my phone) but when I used a tablet I got 800 though my tablet I bigger than my phone. how come? something seems odd and I don't know what it is. any suggestions?