How to Calculate Radius

The radius is the distance from the center of a circle to its edge and is a necessary measure in calculating other dimensions. For example, the area of a circle is the radius squared times the value of Pi (3.1416), and the volume of a sphere is four/thirds times Pi times the radius cubed. Fortunately, the radius is easy to calculate given one other measurement.

Things You'll Need

• Calculator

Instructions

1. Calculate the radius from a known diameter by dividing the diameter in half. For example, a diameter of 20 divided by 2 produces a radius of 10.

2. Calculate the radius from a known circumference by dividing the circumference into twice the value of Pi. For example, a circumference of 20 divided by 6.28 (twice the value of Pi) produces a radius of 3.184.

3. Calculate the radius from a known area by dividing the area by Pi and then finding the square root of the result. For example, an area of 100 divided by 3.14 (Pi) equals 31.83. The square root of 31.83 equals 5.64, which is the radius.

References

• Circle Formulas and Calculator

Resources

• Read this Article in Spanish