There are conversion factors. Within the customary system, with common units, you use12 inches (in) = 1 foot (ft)36 in = 3 ft = 1 yard (yd)792 in = 66 ft = 22 yds = 1 chain7920 in = 660 ft = 220 yds = 10 chains = 1 furlong63360 in = 5280 ft = 1760 yds = 80 chains = 8 furlongs = 1 mile (mi).Within the metric system10 millimetre (mm) = 1 centimetre (cm)100 mm = 10 cm = 1 decimetre (dm)1,000 mm = 100 cm = 10 dm = 1 metre (m)10,000 mm = 1,000 cm = 100 dm = 10 m = 1 decametre (dam)100,000 mm = 10,000 cm = 1,000 dm = 100 m = 10 dam = 1 hectometre (hm)1,000,000 mm = 100,000 cm = 10,000 dm = 1,000 m = 100 dam = 10 hm = 1 kilometre (km).To convert from a smaller unit to a larger one (left to right) you divide by the conversion factor.In both cases there are smaller and larger units. In the case of the customary system they basic unit-to-next unit conversion often requires yet another conversion factor. In the metric system, the conversion factor is 1,000.