Determine the greatest common factor between the two numbers of the ratio. This is the largest number that can divide into both numbers without leaving a remainder. For example, in a 16:20 ratio, the largest common factor is 4.
Do the division on your calculator, using each of the ratio's numbers as the numerator and the greatest common factor as the divisor. On the 16:20 example, this will be (16/4):(24/4).
Replace the previously large numbers with their simpler counterparts. The 16:20 has become 4:5 after both numbers' division by 4.
Repeat the process if the numbers of the simpler form can be divided with a common factor again. A 16:24 ratio can become 4:6, which can become (4/2):(6/2) = 2:3. However, there is an alternate way of simplifying ratios when division between the initial large numbers can give us an integer.
Divide the ratio by using one number as the numerator and the other as the divisor. For instance, on the 23:92, divide 92 by 23 = 4. Whenever the quotient is an integer, then the ratio will be simplified by replacing the old numbers with 1 and the integer, or 1:4.