Area of a Circle Calculator
Calculate the area of a circle given its radius (or diameter). A = πr².
Result
Area
78.5398 units²
r = 5, π ≈ 3.14159265.
- Radius5
- Diameter10
- Circumference31.4159
- Area in terms of π25 π
Step-by-step
- Use radius: 5.
- Area = π × r² = π × 5² = π × 25 = 78.5398.
How to use this calculator
- Pick whether you have radius or diameter.
- Enter the value.
- Read the area; the breakdown also shows circumference.
About this calculator
The area of a circle is π times the radius squared. If you know the diameter (twice the radius), divide by 2 first. The classic value of π — 3.14159… — has been computed to trillions of digits, but for engineering purposes 3.14159 (or 3.1416) is more than enough.
Frequently asked
The ratio of any circle's circumference to its diameter — approximately 3.14159265. It's irrational (doesn't terminate or repeat) and transcendental (not the root of any polynomial with rational coefficients).
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