The civilized world uses the metric system. The US seem to remain stuck in their medieval system of feet, inches and yards. Meanwhile designers stick to a completely different system of measurement called points. To confuse things even more, there a PostScript points, pica points and didot points. Weird….

PostScript points

When Adobe created PostScript, they added their own system of points. There are exactly 72 PostScript points in 1 inch.

• 1 PostScript point =0.35277138 mm = 1.00375001 pica point = 0.01388888 inch

Didot points

The didot system originated in France but was used in most of Europe.

• 1 didot point = 0.376065 mm = 1.07007 pica point = 0.0148057 inch
• 1 cicero equals 12 didot points.

Pica points

This system was developed in England and is used in Great-Britain and the US.

• 1 pica point = 0.35146 mm = 0.93457 didot point = 0.013837 inch
• 1 pica equals 12 pica points.

Inches, feet and yards

I don’t know if it is an urban myth but I once read one of the US space rockets exploded because of a mistake caused by a rounding error in a conversion routine between inches and millimetres.

• 1 inch = 25.4 mm
• 1 foot = 12 inch = 304.80 mm
• 1 yard = 3 feet = 914.4 mm

Other sources of information

Convert-Me is a nice site that offers conversion tools for almost everything.