Given 1 in = 2.54 cm, how many centimeters are in a foot?
One foot = 12 inches
Notice how the relation 1 in = 2.54 cm is expressed as 2.54 cm/in, or in words, 2.54 cm per 1 in. Metric conversion units are not usually considered for significant figures because the factors are exact (1m = 100 cm for instance). However because inches are in the English system, the conversion factor from metric is not exact, so significant figures are considered.