Radius calculator
Enter a radius to calculate the circle’s area, diameter and circumference. Choose miles or kilometers, then open the circle on the map.
The map opens at New York. Search or click the map to change the center.
How to calculate area from a radius
For local planning, circle area is approximately π × radius². A 5-mile radius covers about 78.54 square miles; a 10-mile radius covers about 314.16 square miles. Doubling the radius covers roughly four times the area.
| Radius | Diameter | Circle area |
|---|---|---|
| 1 mi | 2 mi | 3.14 sq mi |
| 5 mi | 10 mi | 78.54 sq mi |
| 10 mi | 20 mi | 314.16 sq mi |
| 25 mi | 50 mi | 1,963.49 sq mi |
| 50 mi | 100 mi | 7,853.88 sq mi |
How to show the radius on a map
Enter a radius and choose a unit. Select Show radius on map to open the radius map. Search an address or postal code to change the center. Add circles to compare locations, then export or share the map.
Radius is half the diameter
The radius goes from the center to the edge. The diameter crosses the circle through its center and is twice the radius. For a circle 10 miles across, set a 5-mile radius.
How distances and areas are calculated
Calculations use surface distances on a spherical Earth. Area is A = 4πR² sin²(r / 2R), where R is the mean Earth radius and r is the selected radius. Circumference is 2πR sin(r / R). For small circles, these are close to πr² and 2πr.
Circles do not show driving distance or travel time. Overlapping circles are measured separately. Read data sources and measurements for details about geometry and US ZIP coverage.