Diameter to Radius
Convert any diameter value to its radius instantly. The radius is exactly half the diameter. Enter the diameter below to get the result.
Diameter to Radius Formula
To find the radius from a known diameter, simply divide the diameter by 2:
r = d ÷ 2
The radius r equals the diameter d divided by 2. This is the simplest circle conversion — the radius is always exactly half the diameter.
For example, find the radius of a circle with a diameter of 10:
r = 10 ÷ 2 = 5
The radius of this circle is 5.
Frequently Asked Questions
Divide the diameter by 2. The formula is r = d ÷ 2. For example, a diameter of 10 gives a radius of 5. This works in any unit.
r = 25 ÷ 2 = 12.5. The radius is 12.5 units.
The diameter is the full distance across a circle through its center. The radius is the distance from the center to the edge — exactly half the diameter. If you know one, you can always find the other.