# Circumference Calculator

URL: https://speedycalculator.com/calculators/math/circumference/
Last updated: 2026-10-30

> The circumference calculator finds the distance around a circle from its radius, diameter or area – or the radius from the circumference.

## Inputs

- Radius r (cm, m, mm, in, ft, yd, km, mi)

## Results

- Circumference
- Diameter
- Area
- Circumference in terms of π

## Formula

```
C = 2πr = πd = 2√(πA)
```

## Explanation

The circumference is the perimeter of a circle. It tells you how far a wheel travels in one turn, how long a round fence or table edge is, and how to size a ring or belt.

### How to use the Circumference Calculator

- **Radius r**
- Every result field is editable: type into **Circumference** or any other result and **Radius r** plus every other field update to match.

Results update as you type, and everything is calculated in your browser.

### How it works

Enter the radius or type into the diameter, circumference or area field.

### What each result means

- **Circumference** = 2×pi×[Radius r]
- **Diameter** = 2×[Radius r]
- **Area** = pi×[Radius r]^2
- **Circumference in terms of π** = 2×[Radius r]

### Example values

How the main result changes when **Radius r** changes and everything else stays at the example values above:

Radius r (cm)Circumference (cm)2.515.7083.7523.5619531.41596.2539.26997.547.12391062.8319

## Worked example

Inputs — Radius r: 5 cm.

Results — **Circumference = 31.415927 cm**; Diameter = 10 cm; Area = 78.539816 cm²; Circumference in terms of π = 10 π.

## Key terms

- **Circumference**: The distance around a circle.

## FAQ

**How far does a 70 cm wheel travel per turn?**
π × 70 ≈ 219.9 cm.

**How do I measure circumference?**
Wrap a string or tape around the object.

**What is circumference ÷ diameter?**
Always π.

**Is circumference the same as perimeter?**
Yes, for a circle.


## Sources

- [OpenStax – Prealgebra 2e](https://openstax.org/details/books/prealgebra-2e)
- [OpenStax – Algebra and Trigonometry 2e](https://openstax.org/details/books/algebra-and-trigonometry-2e)
- [Wolfram MathWorld – Circumference](https://mathworld.wolfram.com/Circumference.html)