Circle Area & Circumference Calculator
The area of a circle is π × r² and its circumference is 2 × π × r, where r is the radius. This Circle Area & Circumference Calculator finds both from either the radius or the diameter of the circle — you are only one click away from the answer.
Circle Area & Circumference Calculator
How to use the Circle Area & Circumference Calculator?
The use of the Circle Area & Circumference Calculator is really easy: enter the diameter or the radius of the circle, the result appears immediately.
How to calculate the circle area and circumference
Formulas used for the calculation of a circle’s circumference and area from diameter
- The formula used for the calculation of circumference: C = d ∙ π
- The formula used for the calculation of area: A = (d/2)2 ∙ π
The formula used for the calculation of a circle’s circumference and area from radius
- The formula used for the calculation of circumference: C = 2 ∙ r ∙ π
- The formula used for the calculation of area: A = r2 ∙ π
What is Pi or π?
π is a mathematical constant, approximately equal to 3.1415926535. It is defined in Euclidean geometry as the ratio of a circle’s circumference to its diameter, and also has various equivalent definitions. The number appears in many formulas in all areas of mathematics and physics.
Frequently asked questions
How do you calculate the area of a circle?
Multiply pi by the radius squared: area = π × r². A circle with radius 5 has an area of π × 25 ≈ 78.54.
How do you calculate the circumference of a circle?
Multiply the diameter by pi, or multiply the radius by 2π. A circle with radius 5 has a circumference of 2 × π × 5 ≈ 31.42.
What is the difference between radius and diameter?
The diameter is the distance across a circle through its centre, and the radius is half of that, from the centre to the edge.
How do I find the area from the diameter?
Halve the diameter to get the radius, then use π × r². For a diameter of 10, the radius is 5 and the area is π × 25 ≈ 78.54.
What value of pi does the calculator use?
The calculator uses pi to high precision (about 3.14159), giving accurate results for both area and circumference.