Circumference calculator
Calculate the perimeter of a circle from one known value: diameter, radius, or area
❓ How the calculator works
A circumference is the closed curve bounding a circle. Its length (the circle perimeter) depends on a single parameter: you only need the diameter, radius, or area of the circle.
Choose what you know, enter the value and unit — the calculator instantly shows the circumference in the same linear units (mm, cm, m, or km). For area, the input is in square units of the chosen dimension.
📐 Formulas
From diameter
L = π × d
From radius
L = 2π × R
From area
L = 2√(π × S)
💡 Examples
From diameter: a pipe with 100 mm diameter
- L = π × 100 = 314.16 mm (≈ 314 mm with π ≈ 3.14)
From radius: inner radius 26 mm
- L = 2 × π × 26 = 163.36 mm
From area: circle area 1146.5 m²
- L = 2 × √(π × 1146.5) = ≈ 120 m
✅ Tips
- Pipes have inner and outer diameters — clarify which one you need for the calculation.
- Pi is irrational, so the result is always approximate; precision depends on the pi value used.
- Radius is half the diameter: R = d / 2.
- For a quick estimate use π ≈ 3.14 — as in school problems.