The numbers on a metric ruler are already decimals. The marks on an English ruler may or may not be decimals already, depending on the ruler. Determine what fraction or mixed number the mark represents. Convert the fraction to a decimal by dividing the numerator by the denominator. Example The mark on the ruler below is at 1 1/8. (There are 8 spaces between 1 and 2 of the size of the space between this mark and the previous or next larger mark.) Divide 1 by 8 to determine that the decimal fraction is 0.125. Add the integer part of the number to get the decimal equivalent 1 1/8 = 1.125 