About this calculator
Calculate circle area and circumference from radius or diameter.
Use half the diameter if you only know diameter.
Formula
Area = πr². Circumference = 2πr.
Example
Radius 1m gives area ≈ 3.142m² and circumference ≈ 6.283m.
Accuracy
NUMTX shows the assumptions next to the calculation so you can replace defaults with values that match your situation. For measurements, supplier rates, fees, interest, tax or regulated work, confirm important figures with the appropriate official or professional source.