Circumference and Area of a Circle Calculator
Calculate every property of a circle — circumference, area, radius, diameter — from any single known measurement. Enter a radius, diameter, or area and all other values are derived instantly.
Solve from
C = 2π × radius
A = π × radius²
- 1
Radius (input)
5 - 2
Circumference
2 × π × 5 = 31.4159
How does this calculator work?
A circle is fully described by C = 2πr (circumference) and A = πr² (area). Enter the radius, diameter, or area and all other measurements are calculated. For radius 5: C ≈ 31.42, A ≈ 78.54. Area scales as r², so doubling the radius quadruples the area but only doubles the circumference.
Formula
How this is calculated
A circle is fully defined by a single measurement. This calculator lets you start from any of three: the radius r, the diameter d = 2r, or the area A. From a radius, C = 2πr gives the circumference and A = πr² gives the area. From a diameter, the radius is d/2 first. From an area, the radius is recovered as r = √(A/π), and the circumference follows.
All three quantities involve π ≈ 3.14159, which appears because circumference and area both arise from the rotational symmetry of a circle. Circumference grows linearly with radius; area grows as the square — doubling the radius quadruples the area but only doubles the circumference.
This calculator is unit-agnostic: results are in whatever unit you use for the input. Enter radius in centimetres and circumference is in centimetres; area is in cm². When entering area, note that the unit for area is the square of your length unit — so if the area is 78.54 cm², the radius is 5 cm.
Frequently asked questions
Circumference is the perimeter — the 1-D distance around the edge (C = 2πr, same units as r). Area is the 2-D space inside (A = πr², in square units). For radius 5: C ≈ 31.42 and A ≈ 78.54.
Rearrange A = πr² to r = √(A/π). Select "Area" from the dropdown above and enter the area — the calculator does this automatically.
Doubling the radius doubles the circumference (linear in r) but quadruples the area (proportional to r²). A circle with radius 10 has twice the circumference but four times the area of one with radius 5.
TG we-Calculate Editorial Team. (2026). Circumference and Area of a Circle Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/circumference-area-circle-calculator
TG we-Calculate Editorial Team. "Circumference and Area of a Circle Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/circumference-area-circle-calculator.
TG we-Calculate Editorial Team, "Circumference and Area of a Circle Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/circumference-area-circle-calculator
@misc{wecalculate_circumference_area_circle_calculator, title = {Circumference and Area of a Circle Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/circumference-area-circle-calculator}}, year = {2026}, note = {TG we-Calculate} }
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