Circle Calculator

Free online Circle Calculator with step-by-step solutions. 100% client-side, no data upload.

Enter any one value(radius, diameter, circumference, or area)
ResultsAll circle values
ORD = 2RC = 2πRA = πR²
Circle with center O, radius R, diameter D, circumference C, and area A
Enter a value and click Calculate to see results.
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Circle Calculator

This free online Circle Calculator computes all key properties of a circle from a single input value. 100% client-side, no signup required.

Key Formulas - Diameter: D = 2R - Circumference: C = 2πR = πD - Area: A = πR² = πD²/4
How to use Enter either the radius, diameter, circumference, or area. The calculator instantly computes the remaining three values along with a detailed step-by-step solution.
Applications Circle calculations are used in engineering (gears, pipes, wheels), architecture (domes, arches), physics (circular motion, wave propagation), astronomy (orbits), and everyday life.
Privacy & Performance All calculations run locally in your browser. No data is transmitted, logged, or stored on any server.
🔒 Client-side only⚡ Web Worker processing🌐 Works offline🛡️ Zero server logs

Frequently Asked Questions

Got questions about circles, π, or how to use this calculator? We've got answers.

How does this calculator work?

Enter any one value — radius, diameter, circumference, or area — and the calculator computes the other three using the formulas: D = 2R, C = 2πR, A = πR². Results appear instantly with a step-by-step breakdown.

What is π (pi)?

π (pi) is the ratio of a circle's circumference to its diameter. It is approximately 3.14159265… and is an irrational, transcendental number. It appears in many formulas across geometry, trigonometry, and physics.

Can I enter values in scientific notation?

Yes. You can enter values like "1.5e2" or "3.14e-1" in any input field. The calculator will parse them correctly.

What if I enter multiple values?

Only the first non-empty field (in the order: radius, diameter, circumference, area) is used. The other fields are cleared when you start typing in one.

Is this calculator private?

Yes. All calculations run locally in your browser. No data is transmitted, logged, or stored on any server.