Solve a proportion for the missing value, or convert a distance using a map scale. Two calculators built on the same cross-multiplication rule.
The proportion a : b = c : x says that the products of the outer and inner terms are equal: a · x = b · c. Rearranged, x = (b · c) ÷ a. That single rule settles most questions about scale, recipes and scaling quantities up or down.
A scale of 1 : 50,000 says one centimetre on the map stands for 50,000 centimetres on the ground, which is half a kilometre. The scale calculator converts that straight into metres and kilometres.
Cross-multiply and divide: for 3 : 4 = 9 : x you get x = (4 · 9) ÷ 3 = 12.
Multiply the distance on the map by the scale denominator. 4 cm at 1 : 50,000 is 200,000 cm, or 2 km.
Yes — any percentage question can be written as a proportion in which the whole corresponds to 100. That is why the percentage and proportion calculators solve the same problems from two directions.
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