When you need this conversion
Checking whether type will be legible on a physical object, matching a font size to a regulation that specifies millimeters (food labels and medicine packaging often do), or setting rules and strokes where the spec is metric but your software works in points.
What “12 pt” actually measures
A font size is the height of the em square, the invisible box each glyph is designed in. It isn’t the height of any particular letter. 12 pt type has a 4.23 mm em, but its capital H might be 3 mm and its lowercase x about 2.2 mm, depending on the typeface. To hit a minimum x-height or cap height, measure a printed sample or check the font’s metrics.
Common sizes
- 6 pt = 2.11667 mm (fine print)
- 8 pt = 2.82222 mm
- 10 pt = 3.52778 mm
- 12 pt = 4.23333 mm
- 24 pt = 8.46667 mm
- 72 pt = 25.4 mm (one inch)
Common mistakes
Treating font size as letter height. A regulation asking for “1.2 mm minimum x-height” isn’t met by 1.2 mm type. The font size will need to be roughly twice that.
Mixing point systems. Old type specimens may use traditional or Didot points. Everything digital uses the 1/72 inch point, which is what this converter uses.
The reverse is millimeters to points.