Circumference Calculator — Circle Perimeter
Find the circumference (perimeter) of a circle instantly. Enter either the radius or the diameter and get the circumference, area, and all related measurements using the exact value of π.
Input type
C = 2π × radius
- 1
Radius (input)
7 - 2
Circumference
2 × π × 7 = 43.9823
How does this calculator work?
The circumference of a circle is C = 2πr = πd, where r is the radius and d is the diameter. For radius 7: C = 2π × 7 ≈ 43.98. The area is A = πr² ≈ 153.94. Enter any radius or diameter to compute circumference, area, and diameter simultaneously.
Formula
How this is calculated
The circumference of a circle is the distance around it — the circle's equivalent of a polygon's perimeter. It is calculated as C = 2πr, where r is the radius (the distance from the centre to any point on the edge). Equivalently, since the diameter d = 2r, you can write C = πd.
π (pi) is an irrational constant ≈ 3.14159, defined as the ratio of circumference to diameter for any circle. It is the same for every circle regardless of size. This calculator uses JavaScript's Math.PI (good to about 15 significant figures) for maximum precision.
If you enter the diameter, the calculator halves it to get the radius before applying the formula. The area A = πr² is shown as a bonus — both circumference and area depend only on the radius. The result is in the same length unit as your input; if you enter centimetres, the circumference is in centimetres.
Frequently asked questions
C = 2π × 5 = 10π ≈ 31.4159. You can verify by entering 5 in the radius field above.
Use C = πd. If the diameter is 14, the circumference is 14π ≈ 43.98. Switch the selector to "Diameter" and enter 14.
Circumference (C = 2πr) is the length of the boundary — a 1D measurement in the same units as the radius. Area (A = πr²) is the amount of flat space enclosed — a 2D measurement in square units.
TG we-Calculate Editorial Team. (2026). Circumference Calculator — Circle Perimeter [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/circumference-calculator
TG we-Calculate Editorial Team. "Circumference Calculator — Circle Perimeter." TG we-Calculate. 2026. https://we-calculate.com/calculator/circumference-calculator.
TG we-Calculate Editorial Team, "Circumference Calculator — Circle Perimeter," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/circumference-calculator
@misc{wecalculate_circumference_calculator, title = {Circumference Calculator — Circle Perimeter}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/circumference-calculator}}, year = {2026}, note = {TG we-Calculate} }
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