TextRenderer.MeasureText and Graphics.MeasureString mismatch in size

This is not a rounding problem. Difference ~ 5+ pixels.

Test Case String: ""MACD (26,12,9) -0.000016"

e.Graphics.MeasureString("MACD (26,12,9) -0.000016", SystemFonts.DefaultFont).Width)
TextRenderer.MeasureText("MACD (26,12,9) -0.000016", SystemFonts.DefaultFont).Width)

The result is always:

139.3942
134

Why is there so much difference in size? I just need the round of width of string outside paint method. But it should match MeasureString or vice versa.

TextRenderer uses GDI to render the text, whereas Graphics uses GDI+. The two use a slightly different method for laying out text so the sizes are different.

Which one you should use depends on what will eventually be used to actually draw the text. If you are drawing it with GDI+ Graphics.DrawString, measure using Graphics.MeasureString. If you are drawing using GDI TextRenderer.DrawText, measure using TextRenderer.MeasureText.

If the text will be displayed inside a Windows Forms control, it uses TextRenderer if UseCompatibleTextRendering is set to false (which is the default).

Reading between the lines of your question, you seem to be using TextRenderer because you don't have a Graphics instance outside the Paint event. If that's the case, you can create one yourself to do the measuring:

using( Graphics g = someControl.CreateGraphics() )
{
    SizeF size = g.MeasureString("some text", SystemFonts.DefaultFont);
}

If you don't have access to a control to create the graphics instance you can use this to create one for the screen, which works fine for measurement purposes.

using( Graphics g = Graphics.FromHwnd(IntPtr.Zero) )
{
     SizeF size = g.MeasureString("some text", SystemFonts.DefaultFont);
}

I Made the following class to use MeasureString outside the paint event, and it works pretty well.

public interface ITextMeasurer
    {
        SizeF MeasureString(string text, Font font, StringFormat format);
    }

    public class TextMeasurer : ITextMeasurer
    {
        private readonly Image _fakeImage;
        private readonly Graphics _graphics;

        public TextMeasurer()
        {
            _fakeImage = new Bitmap(1, 1);
            _graphics = Graphics.FromImage(_fakeImage);
        }

        public SizeF MeasureString(string text, Font font, StringFormat format)
        {
            return _graphics.MeasureString(text, font, int.MaxValue, format);
        }
    }