Convert Pixels to Points

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();

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%).

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

System.Drawing.Graphics has DpiX and DpiY properties. DpiX is pixels per inch horizontally. DpiY is pixels per inch vertically. Use those to convert from points (72 points per inch) to pixels.

Ex: 14 horizontal points = (14 * DpiX) / 72 pixels

Surely this whole question should be:

"How do I obtain the horizontal and vertical PPI (Pixels Per Inch) of the monitor?"

There are 72 points in an inch (by definition, a "point" is defined as 1/72nd of an inch, likewise a "pica" is defined as 1/72nd of a foot). With these two bits of information you can convert from px to pt and back very easily.

Using wxPython on Mac to get the correct DPI as follows:

    from wx import ScreenDC
    from wx import Size

    size: Size = ScreenDC().GetPPI()
    print(f'x-DPI: {size.GetWidth()} y-DPI: {size.GetHeight()}')

This yields:

x-DPI: 72 y-DPI: 72

Thus, the formula is:

points: int = (pixelNumber * 72) // 72