⭕Circle Calculator
Enter any one value — radius, diameter, circumference, or area — to find the rest, or switch to arc/sector mode.
Free Circle Calculator
Know just one measurement of a circle? Our free circle calculator finds the rest instantly. Enter the radius, diameter, circumference, or area — any one value — and get all four calculated immediately, shown both as exact π-expressions (like 25π) and decimals, with a to-scale diagram.
Need arc length or sector area instead? Switch to arc/sector mode, enter a radius and a central angle, and get the arc length, sector area, and chord length for that slice of the circle, with the sector highlighted visually.
Every formula used is shown step by step, including the algebra to reverse-solve for radius when you start from area or circumference. No sign-up, no downloads — just enter what you know and solve. See the About page or the FAQ for more.