A range is an interval that defines the minimum and maximum values for any set of numbers or for the variation of a particular variable -- a stock price on the market, for example. The per cent relative range refers to the percentage ratio of the range to the average value in the set.

Sum up the maximum and minimum values in the range. For example, if the stock price changes in the range from £22.5 to £26.7 then £22.5 + £26.7 = £49.2.

Divide the sum by two to calculate the average value. In the example, the average price is £49.2 /2 = £24.6.

Subtract the minimum value from maximum one to calculate the range. In this example, the range is £26.7 - £22.5 = £4.10.

Divide the range by the average value, and then multiply the result by 100 to calculate the relative per cent range. In this example, the relative per cent range is ($6.44 / £24.6) x 100 = 16.99 per cent.