Enter a circle's radius, diameter, circumference or area to get all four measurements, calculated with the full precision of pi.
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Enter your numbers to see a result.
With i know the Radius, value 5, the area is 78.53981634.
| I know the | Radius |
|---|---|
| Value | 5 |
| Area | 78.53981634 |
|---|---|
| Radius | 5 |
| Diameter | 10 |
| Circumference | 31.41592654 |
| Area | 78.53981634 |
Choose the measurement you already know and enter it. The calculator turns it into the radius, then works out the diameter, circumference and area. Pi is used to full double precision (3.141592653589793), not rounded to 3.14, which matters for large circles.
Diameter = 2r. Circumference = 2πr. Area = πr². From an area A, r = √(A ÷ π). Choose the measurement you already know and enter it. The calculator turns it into the radius, then works out the diameter, circumference and area. Pi is used to full double precision (3.141592653589793), not rounded to 3.14, which matters for large circles.
With i know the Radius, value 5, the area is 78.53981634. Radius: 5; Diameter: 10; Circumference: 31.41592654; Area: 78.53981634.
This is an estimate based on the inputs and assumptions shown on this page, not professional advice. Check anything with financial, health or safety consequences independently.
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Halve the diameter to get the radius, then multiply π by the radius squared. A 10 cm diameter gives r = 5 cm and an area of about 78.54 cm².
Divide the circumference by π. A circumference of 100 cm gives a diameter of about 31.83 cm.
No. Area grows with the square of the radius, so doubling the radius makes the area four times larger, while the circumference only doubles.