What Is the Diameter to Radius Calculator?
This calculator converts a circle's diameter into its radius. The diameter is the straight-line distance across a circle passing through its center, while the radius is the distance from the center to the edge. Because the diameter spans the full circle and the radius spans only half, the radius is always exactly half the diameter.
How to Use It
Enter the diameter of your circle in any unit of measurement (centimeters, inches, meters, etc.) and the calculator instantly returns the radius in the same unit. There is no need to specify the unit—the relationship \(r = d/2\) holds for any consistent unit.
The Formula Explained
The conversion uses the formula $$r = \frac{d}{2}$$ where r is the radius and d is the diameter. Since the diameter is two radii laid end to end across the center, dividing it by two recovers a single radius. Likewise, you can reverse the relationship with \(d = 2r\).
Worked Example
Suppose a pizza has a diameter of 14 inches. To find the radius, divide by two: $$r = \frac{14}{2} = 7 \text{ inches}$$ The crust sits 7 inches from the center in every direction.
FAQ
Is the radius always half the diameter? Yes. For any circle, the radius is exactly one half of the diameter.
What unit is the answer in? The radius is returned in the same unit you entered the diameter in.
How do I go from radius back to diameter? Multiply the radius by 2: \(d = 2 \times r\).
