Convert Pixels to Points

Question

There are 72 points per inch; if it is sufficient to assume 96 pixels per inch, the formula is rather simple:

points = pixels * 72 / 96

There is a way to get the configured pixels per inch of your display in Windows using GetDeviceCaps. Microsoft has a guide called "Developing DPI-Aware Applications", look for the section "Creating DPI-Aware Fonts".

The W3C has defined the pixel measurement px as exactly 1/96th of 1in regardless of the actual resolution of your display, so the above formula should be good for all web work.

Try this if your code lies in a form:

Graphics g = this.CreateGraphics();
points = pixels * 72 / g.DpiX;
g.Dispose();

Starting with the given:

• There are 72 points in an inch (that is what a point is, 1/72 of an inch)
• on a system set for 150dpi, there are 150 pixels per inch.
• 1 in = 72pt = 150px (for 150dpi setting)

If you want to find points (pt) based on pixels (px):

 72 pt    x pt
------ = -----                  (1) for 150dpi system
150 px    y px

Rearranging:

x = (y/150) * 72                (2) for 150dpi system

so:

points = (pixels / 150) * 72    (3) for 150dpi system

Assuming 96dpi is a huge mistake. Even if the assumption is right, there's also an option to scale fonts. So a font set for 10pts may actually be shown as if it's 12.5pt (125%).

WPF converts points to pixels with the System.Windows.FontSizeConverter. The FontSizeConverter uses the System.Windows.LengthConverter. The LengthConverter uses the factor 1.333333333333333333 to convert from points (p) to pixels (x): x = p * 1.3333333333333333