This free map scale converter tool lets you convert between absolute and relative scales using any units (mm, cm, m, km, inches, feet, yards, miles). You can choose the units to be converted to or from and get the absolute or relative values. The app also lets you use decimals in the numbers.
An absolute scale is a scale that is unitless ratio that indicates how condensed a map is; how many units of the actual surface of the earth is represented by one unit on the map, eg. "1:10000". Absolute scales are often referred to as ratios or representative fractions. A relative scale on the other hand is similar in that it is a ratio, however, it includes a specific unit of measurement for both portions of the ratio, eg. "1cm:1km". Relative scales can also be written in a word statement, such as "One centimeter equals one kilometer".
Every map has (or should have) a scale that indicates how much one unit of the map represents in the real world. Anyone who reads maps may want to more easily deal with the conversion with an app like this. Also, cartographers, mappers, Geographic Information Systems (GIS) technicians and specialists also need to convert between map scales on a regular basis when designing new maps. Model builders that design models for cars, planes, ships etc. may also like to easily convert between an absolute measurement and a relative.