---
title: "Circle Calculator — Radius, Diameter, Circumference, Area"
description: "Calculate all circle properties from any one value. Enter radius, diameter, circumference, or area to get all others. Free circle calculator with formulas."
url: "https://worldcalculators.org/calculators/circle/"
canonical: "https://worldcalculators.org/calculators/circle/"
---

# Circle Calculator

Calculate all circle properties from any one value. Enter radius, diameter, circumference, or area to get all others. Free circle calculator with formulas.

## Quick answer

Radius (r) : half the diameter. Circumference = 2πr = πd. Area = πr². From area: r = √(A/π). From circumference: r = C/(2π). π = 3.14159265...

## How π is Used in Education by Country

* German/French use comma as decimal separator (3,14 not 3.14)

## Frequently Asked Questions

From circumference C: first find r = C/(2π), then A = πr². Or directly: A = C² / (4π). Example: C = 20 cm → r = 20/(2π) ≈ 3.183 cm → A ≈ 31.83 cm².
Diameter = 2 × radius. The radius is the distance from the centre to the edge. The diameter is the distance across the circle through its centre. Formula connection: C = πd = 2πr.

Source: https://worldcalculators.org/calculators/circle/
Markdown mirror of the HTML page. Prefer this URL for RAG; the interactive calculator still lives on the HTML page.