Radius From Diameter

Radius from Diameter

To find the radius when you know the diameter, use the fact that the radius is half of the diameter.

Method

1. Identify the diameter in the problem.
2. Divide it by 2.
3. Simplify the result if possible.

Why this works

The diameter goes all the way across a circle through its center. The radius goes from the center to the edge, so two radii make one diameter.

Example pattern

• If the diameter is 10, then the radius is 10 ÷ 2 = 5.
• If the diameter is 7, then the radius is 7 ÷ 2 = 3.5.

Check your answer

Make sure that:

• the radius is half of the diameter,
• doubling your radius gives back the original diameter.

If your answer is an exact fraction or decimal, leave it in simplest form.