Area of a Circle Calculator
This calculator works out the area, circumference and diameter of a circle from just one measurement, using the standard formula A = πr². Knowing a circle's area is useful for everyday and trade tasks, from working out how much turf, paint or fabric covers a circular space, to schoolwork on geometry, to trade jobs like sizing a pipe or a circular garden bed. To use it, choose whether you are entering the radius (the distance from the centre to the edge) or the diameter (the distance straight across the circle), type in your measurement, and pick the unit you are working in, from millimetres and centimetres through to metres, feet, inches and miles. The calculator instantly returns the area (highlighted in square units), the circumference, and the diameter and radius, so you can check your figures converted the right way. You can also choose how many decimal places to show, handy if you need extra precision for technical work or just a rounded figure for a quick job. Below the results, a step-by-step working panel shows exactly how pi was multiplied through to reach the final area and circumference, so you can follow the maths or check your own working by hand. Because the calculation uses a fixed geometric formula rather than an estimate, the figures are exact to the precision you choose.
