Area of Circle Calculator

Calculate circle area from radius or diameter. Free online circle area calculator with pi-based formula.

The Area of Circle Calculator computes the area enclosed by a circle using either the radius or diameter. This essential geometry tool applies the formula A = πr² to give you precise results for circular spaces, plates, wheels, and any round objects. Perfect for construction, manufacturing, design, and academic applications involving circular shapes.

Common use cases

  • Pizza size comparisons
  • Circular pool or fountain areas
  • Wheel and tire surface calculations
  • Pipe cross-section areas
  • Circular garden bed planning

How to use

  1. Enter the radius OR diameter
  2. Select which measurement you're providing
  3. Click calculate for the area
  4. View the calculation with π
  5. Copy the precise result

FAQ

What is the formula for circle area?

Area = πr², where r is the radius. With diameter d: Area = π(d/2)² = πd²/4.

Why does area use π?

Pi (π ≈ 3.14159) is the ratio of circumference to diameter, fundamental to all circle calculations.

Does doubling the radius double the area?

No, area quadruples! Since area ∝ r², doubling r gives 4× the area.

How accurate is the result?

Our calculator uses high precision for π. Results are accurate to many decimal places.