Convert foot to decameter

The inch has been exactly 2.54 cm since 1959; 12 inches make a foot, 3 feet a yard and 1,760 yards a mile of 1.609 km. The US and UK still use them for heights (5 ft 10 in is 178 cm), road distances and speed limits, and the inch survives everywhere in screen sizes, wheel rims and pipe threads. Five miles are almost exactly eight kilometres, a handy road-sign rule.

The in-between metric units are taught at school and then mostly forgotten – except regionally. Dutch motorways carry a 'hectometre post' every 100 m, so traffic news and breakdown services place a jam at 'A2, hectometre post 57.3'. In Sweden and Norway the decimetre is an everyday word, a half-decimetre being about two inches, and the decilitre does the same job in Nordic recipes. The decametre is the odd one out: 10 m is about the length of a bus, and the unit is hardly used anywhere.