When you create a custom ASP.NET control most of the times you inherit it from WebControl class or one of it's derivatives. Among other properties WebControl has a Font property of FontInfo type which in turn has a Size property of FontUnit type. Users can set the yourControl.Font.Size to any HTML/CSS compatible value from 12pt to 1.2em to x-large.

This is all fine while your control outputs plain HTML. But at this moment I'm working on a controls which use Flash controls as their output and Flash knows nothing about font sizes in points let alone x-small & co. (at least I was told so by my flash developer colleague). So what I needed was a way to convert all the reasonable FontUnit values to some more or less equivalent pixel sizes. So after some experiments I came up with this FontSizeConverter class with only one static method to convert FontUnit to pixels.

Keep in mind that this is only a raw approximation and doesn't pretend to be completely correct and universal solution. Em and Percentage values use 16px as base.

public class FontSizeConverter
{
    public static int ToPixels(FontUnit unitSize)
    {
        int result = 16;

        if (unitSize.Type != FontSize.NotSet && unitSize.Type != FontSize.AsUnit)
        {
            // size in x-small, etc
            switch (unitSize.Type)
            {
                case FontSize.XXSmall:
                    result = 9;
                    break;
                case FontSize.XSmall:
                    result = 10;
                    break;
                case FontSize.Smaller:
                case FontSize.Small:
                    result = 13;
                    break;
                case FontSize.Medium:
                    result = 16;
                    break;
                case FontSize.Large:
                case FontSize.Larger:
                    result = 18;
                    break;
                case FontSize.XLarge:
                    result = 24;
                    break;
                case FontSize.XXLarge:
                    result = 32;
                    break;
                default:
                    result = 16;
                    break;
            }
        }
        else if (unitSize.Type == FontSize.AsUnit)
        {
            switch (unitSize.Unit.Type)
            {
                case UnitType.Pixel:
                    result = (int)Math.Round(unitSize.Unit.Value);
                    break;
                case UnitType.Point:
                    result = (int)Math.Round(unitSize.Unit.Value*1.33);
                    break;
                case UnitType.Em:
                    result = (int)Math.Round(unitSize.Unit.Value * 16);
                    break;
                case UnitType.Percentage:
                    result = (int)Math.Round(unitSize.Unit.Value * 16 / 100);
                    break;
                default:
                    // other types are not supported. just return the medium
                    result = 16;
                    break;
            }
        }

        return result;
    }
}