Area of a Circle Calculator
Square the radius and multiply by π (about 3.14159). The circle calculator also works backwards from diameter, circumference or area.
A = πr²
Perimeter: C = 2πr
Area of the circle
50.2655ft²
- Circumference
- 25.1327 ft
- A = π × 4² = 50.2655 ft²
- C = 2 × π × 4 = 25.1327 ft
Area in other units
| m² | 4.6698 |
| cm² | 46,698.2 |
| ft² | 50.2655 |
| in² | 7,238.23 |
| yd² | 5.5851 |
| acres | 0.001154 |
| hectares | 0.000467 |
How to find the area of a circle
Formula: A = πr². Perimeter: C = 2πr.
- Measure every length in the same unit. Mixing feet and inches is the most common mistake; convert first (6 in = 0.5 ft).
- Put the numbers into the formula above. The calculator shows each substitution with your numbers.
- Area comes out in square units (ft², m²). If you need a different unit, open "Area in other units".
Why the area of a circle is πr²
Cut a circle into wedges like a pizza and lay them tip-to-tail. The more slices, the closer the strip gets to a rectangle: its height is the radius r, and its length is half the circumference, πr. So the area is πr × r = πr².
Strip ≈ 3.142r long × r tall
Questions people ask
I have the diameter, not the radius.
Halve it first. A 10 in pizza has r = 5 in, so A = π × 25 ≈ 78.54 in².
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Paste a homework question or describe your project. The AI tutor names the formula and works it through step by step. Always check the result with the calculator above.
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