Facts

The metric system measures length in metres m. The prefixes centi- (one-hundredth) and milli- (one-thousandth) can be used to zoom in, so

1 m = 100 cm = 1,000 mm,    1 cm = 10 mm.

The imperial units are yards yd, feet ft, and inches in, where

1 yd = 3 ft = 36 in,    1 ft = 12 in,    1 in = 0.0833 ft.

Converting between them,

1 cm = 0.3937 in,    1 in = 2.5400 cm.

The imperial system does not use a prefix structure, so fractions are often used. Here are the commonest:

1/2 = 0.5000,    1/4 = 0.2500,    1/8 = 0.1250,    1/16 = 0.0625,    1/32 = 0.0313.

Calculator

Here's a calculator for quick conversions: