These are two very helpful JavaScript functions if you need to work with ranges and percents.

rangeToPercent

function rangeToPercent(number, min, max){
   return ((number - min) / (max - min));
}

This function returns percentage of a number in a given range. For example rangeToPercent(40,20,60) will return 0.5 (50%). rangeToPercent(34,0,100) will return 0.34 (34%)

percentToRange

function percentToRange(percent, min, max) {
   return((max - min) * percent + min);
}

This function returns number that corresponds to the percentage in a given range. For example percentToRange(0.34,0,100) will return 34.

 

Credits:

Original functions are part of  MathUtils Class by Bruno Imbrizi written in ActionScript3.