Maths Range To Percentage

If you want to go from a value to a percentage, eg from 63.5 to 50%, divide your value by 127 & multiply by 100.

If you want to go the other way, eg from 50% to 63.5, it's the reverse: divide your percentage by 100 & multiply by 127.

While Jon's answer was not incorrect, the answer given by belisarius was more complete, in that it allowed for a range of numbers beginning and ending with any number, and not necessarily starting with 0.

Here's a little better way to represent the formula:

percentage = (value - min) / (max - min)

If you want to represent the percentage as a whole number instead of a decimal, simply multiply the result by 100.

And here's the reverse (going from a percentage to a value):

value = ((max - min) * percentage) + min

The percentage here is a decimal. If your percentage is a whole number, simply divide it by 100 before inserting in this formula.

Generally, if you have numbers in the interval [a,b], to get the percentage inside your interval, the formula is:

percentage = 100 * (x-a) / (b-a)  

Where x is your value