How to Calculate Ratios

A ratio is a proportion of one quantity to another or a group of items to one another. It is a constant that holds true unless the quantities involved change. Ratios are written with a colon, such as 2:1, which is read as 2 to 1.

An example follows each step in parentheses. First we create a ratio. Then we use the ratio.

Instructions

Calculating Ratios

1. Start with a question or scenario involving two or more quantities. (A toy line is sold in cases of two sets with 14 items of 3 different sizes: eight small, four medium, and two large. What is the ratio of the three toy sizes in each case? How many of each size toy is in 15 cases?)

2. Write down all of the quantities involved. (Eight small, four medium and two large)

3. Write quantities next to each other, with a colon between them. (8:4:2)

4. Reduce the ratio like a fraction, if possible. (4:2:1)

Using Ratios

1. Start with a question or scenario. (How many of each size toy is in 15 cases?)

2. Write down the ratio. (4:2:1)

3. Multiply the ratio by the number of sets of items involved. (4:2:1 x 15 cases = 60:30:15)