Enter the radius of a circle and this calculator gives you its area, circumference and diameter.
Result
This result is an estimate only. Check with your bank or the relevant authority before making decisions.
How it is calculated
Area, A = π × r²
Circumference, C = 2 × π × r
Diameter = 2 × r
Here r is the radius and π is about 3.14159. Results are shown to two decimal places.
Worked example
Radius 7:
Area = π × 7² = 153.94
Circumference = 2 × π × 7 = 43.98
Diameter = 2 × 7 = 14.00
Why your number may differ
In school, π is often taken as 22/7, which is only an approximation. This calculator uses a more precise π, so your answer may differ slightly from an answer key that uses 22/7. Results are also rounded to two decimal places.
Frequently asked questions
What is the difference between radius and diameter?
The diameter is twice the radius. A radius of 7 means a diameter of 14.
Can I use 22/7 for π?
22/7 is a school approximation of π. This calculator uses a more precise value of π, so its answer can differ slightly from one worked out with 22/7.
What units is the answer in?
The circumference and diameter are in the same unit as your radius. The area is in square units, for example cm² if the radius is in cm.