Circle Area Calculator | Radius, Diameter or Circumference
Calculate the area of a circle from its radius, diameter, or circumference. See the exact working and watch a visual chart update instantly.
Calculator
Use a period or comma as the decimal separator.
Geometric Overview
Enter a value on the left to see the visualization
How does it work?
The calculator uses standard geometric formulas. Choose an input type above and it automatically converts your value to find the area (A = πr²).
About the circle area calculator
This calculator is a handy tool for students, tradespeople, and hobbyists alike. It uses the classic formula A = πr² to work out the surface enclosed by a circle.
You don't need to know the radius up front. The tool is flexible and lets you start from whichever measurement you already have:
- Radius: the distance from the center to the edge.
- Diameter: the distance straight across the circle through the center (twice the radius).
- Circumference: the total length around the circle's edge.
Everyday uses
Whether you're sizing a round rug for the living room, planning a circular flower bed in the garden, or working out how much paint a round tabletop needs, this calculator gets you the answer fast. Enter one measurement and the area appears instantly, which makes it easy to estimate materials like fabric, soil, or paint.
Frequently asked questions
What is the formula for the area of a circle?
The area of a circle is A = πr², where A is the area, π (pi) is roughly 3.14159, and r is the radius — the distance from the center to the edge.
What is the difference between radius and diameter?
The radius runs from the center of the circle out to the edge. The diameter runs straight across the circle through the center. The diameter is always twice the radius (d = 2r).
How do I find the area if I only know the circumference?
If you know the circumference (C), use the formula A = C² / (4π). The calculator handles this for you automatically when you pick the "Circumference" tab.