Circle Calculator
Area, circumference, diameter — and 90° arc & sector — from radius.
See how it works
Watch a quick simulation of this tool in action — no file needed.
How to use Circle Calculator
Follow these steps — everything happens instantly in your browser.
- 1
Step 1. Enter the radius (any positive number).
- 2
Step 2. See diameter, circumference, area, 90° arc and 90° sector update instantly.
Why use this tool
Private by design
All processing happens locally in your browser. Open DevTools → Network and you'll see zero file uploads. Ever.
Instant
No upload wait, no queue, no server round-trip. Results appear the moment you drop a file.
Free & unlimited
No accounts, no watermarks, no daily caps. Use it as many times as you like, forever.
Works everywhere
Desktop, tablet or phone — every tool is responsive and installable as a PWA for offline use.
Frequently asked questions
Everything you might want to know about circle calculator.
Triangle Calculator
Area (Heron's), perimeter and angles from three sides.
Pythagorean Theorem Calculator
a² + b² = c² — solve for any side of a right triangle.
Projectile Motion Calculator
Range, max height, time of flight — for any launch angle and velocity.
Quadratic Equation Solver
Solve ax² + bx + c = 0 — real and complex roots, with discriminant.