Circle Calculator
Enter any one of a circle's radius, diameter, circumference or area to find the others.
Change the values and press Calculate to work out your own figures.
Enter any one of the radius, diameter, circumference or area.
| Amount | Unit |
|---|---|
| 0.2026829916 | m² |
| 2,026.829916 | cm² |
| 2.181661565 | ft² |
| 314.1592654 | in² |
| 0.2424068406 | yd² |
| 5.008405797e-5 | acres |
Show the working
- d = 2r, C = 2πr, A = πr²
- Area = 314.1592654 in²
How to use it
Enter any one of the radius, diameter, circumference or area.
Enter the measurements (decimals, fractions such as 3/4, or mixed numbers such as 1 1/2) and, if you like, their unit; the answer is then also given in other units. Show the working gives the formula.
Key facts
d = 2r; C = 2πr; A = πr²
From the circumference
r = C ÷ 2π, so a circumference of 31.4159 is a radius of almost exactly 5.
Questions
What is the area of a circle with radius 10?
100π ≈ 314.1592654.
How do I get the radius from the area?
r = √(A ÷ π).
Formulas
d = 2r; C = 2πr; A = πr²
Sources
Limitations
- All measurements in one calculation use the same unit; the answer is also given in other units.
- Measurements up to 10¹⁵.