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Circle Calculator
About the Circle Calculator
Enter any one property of a circle (radius, diameter, circumference or area) and get all the others.
How to use the Circle Calculator
- Enter one of Radius (r), Diameter (d), Circumference (C) or Area (A).
- Press Plot to see the other values and a drawing.
Formula and method
d = 2r Β· C = 2Οr = Οd Β· A = ΟrΒ²
Worked example
For r = 7: d = 14, C = 2Ο Γ 7 β 43.98 and A = Ο Γ 49 β 153.94.
A radius of 4. Area = Ο Γ 4Β² β 50.27, circumference = 2Ο Γ 4 β 25.13 and diameter = 8.
When to use the Circle Calculator
- Finding the area, circumference or diameter from any one measurement.
- Sizing round tables, pipes, pizzas and pools.
- Doing geometry homework.
Common mistakes to avoid
- Mixing up radius and diameter. The diameter is twice the radius.
- Forgetting that area is in square units, while circumference is in ordinary units.
Tips
- Pi (Ο) is about 3.14159. Using more digits gives a more accurate answer.
Frequently Asked Questions
Circumference divided by diameter is always Ο, for every circle.
About 3.14159265, which is more precise than the commonly rounded 3.14.
Radius = β(area Γ· Ο).