Math

Circumference Calculator

Circle circumference from radius or diameter.

Enter your values

Radius

Enter the radius you are working with.

Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.

Results

Circumference: 37.6991
Diameter: 12
Area: 113.0973
Radius: 6

Working

1C = 2π × 6 = 37.6991

Quick answer

Circumference equals 2πr, or πd if you know the diameter.

C = 2πr = πd

At a glance

What it does	Circle circumference from radius or diameter.
Category	Math
Inputs needed	Radius
Main output	Circumference
Formula	C = 2πr = πd
Cost	Free — no sign-up, no download

How to use the Circumference Calculator

1Enter the radius of the circle.
2Read the circumference and area.
3Halve the diameter first if that is what you have.

Inputs explained

Radius: Enter the radius you are working with.

Worked example

Using the values the calculator loads with:

Inputs

Radius6

Results

Circumference37.6991
Diameter12
Area113.0973
Radius6

C = 2π × 6 = 37.6991

Frequently asked questions

What is π?

The ratio of circumference to diameter, about 3.14159.

How do I get radius from circumference?

Divide by 2π.

What do I need to enter into the Circumference Calculator?

Just 1 value: radius. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.

How does the Circumference Calculator work out the answer?

Circumference equals 2πr, or πd if you know the diameter. It applies the formula C = 2πr = πd and shows the working so you can check each step by hand.

Is the Circumference Calculator free, and do I need an account?

It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.

Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.