Scientists Say: Ratio

Ratio (noun, “RAY-shee-oh”)

A ratio is a way to compare two numbers.

Imagine you are baking cookies. The recipe calls for 1 cup of sugar and 2 cups of flour. That means your sugar-to-flour ratio is 1:2.

Here’s why that’s useful. The ratio means tasty cookies contain twice as much flour as sugar. That remains true whether you make one batch of cookies or 20. So you can use ratios to scale recipes up and down while keeping the right mix of ingredients.

You can express a ratio in several ways. One way is to separate the numbers with a colon. You can also use a fraction. For example, rather than describing the sugar-to-flour ratio as 1:2, you could say ½.

Ratios play crucial roles in many fields of science. In chemistry, a material’s density is the ratio of its mass to its volume. Ratios also help chemists scale up and down chemical reactions. In ecology, ratios help describe and monitor animal populations.

Geometry makes use of a famous ratio called pi, or π. One side of the ratio is the distance around — or circumference of — a circle. The other side is the straight-line distance across — or diameter of — the circle. This ratio is about 22:7, or 22/7, for all circles no matter their size.

Let’s unpack what that means. If you measure a circle’s diameter to be 7 centimeters (2.8 inches), you can assume its circumference will be 22 centimeters (8.7 inches). Double the circle’s diameter, and you also double its circumference. This relationship allows us to calculate a circle’s circumference from its diameter and vice versa.

In a sentence

For the most sustainable population, giant water bug farmers strive to maintain a 1:1 male-to-female insect ratio.

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