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Circle Calculator
Enter any one property of a circle (radius, diameter, circumference or area) and get all the others.
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 · C = 2πr = πd · A = πr²
Worked example
For r = 7: d = 14, C = 2π × 7 ≈ 43.98 and A = π × 49 ≈ 153.94.
A radius of 4. Area = π × 4² ≈ 50.27, circumference = 2π × 4 ≈ 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 (π) is about 3.14159. Using more digits gives a more accurate answer.
Frequently asked questions
What is the relationship between circumference and diameter?
Circumference divided by diameter is always π, for every circle.
What value of pi does it use?
About 3.14159265, which is more precise than the commonly rounded 3.14.
How do I find the radius from the area?
Radius = √(area ÷ π).