How it works
Square the radius and multiply by π. The calculator uses a high-precision π constant and passes units through as squares.
Formula
A = πr² = π(d/2)²
How to use Area of a Circle Calculator
- Enter radius, or diameter if the tool accepts either.
- If using diameter, the tool halves it before applying πr².
- Read area in square units (e.g. ft², m²).
- Compare with other shape area tools for composite figures.
Worked examples
Concrete numbers and cases you can check against the tool above.
Garden bed, radius 4 ft
A = π×16 ≈ 50.27 ft² of mulch coverage for a full circle.
When to use Area of a Circle Calculator
Circle area appears in landscaping, pizza sizing, and pipe cross-sections. Diameter-to-radius mistakes are common without a dedicated step.
Common use cases
- Estimate sod or mulch for a circular garden bed.
- Find cross-sectional area of a round duct or pipe.
- Solve geometry problems involving semicircles (use half the result).
Inputs and outputs
- Radius or diameter in any consistent length unit
Privacy
This tool runs entirely in your browser. Your data never leaves your device — nothing is uploaded to our servers.
Frequently asked questions
- Which value should I enter — radius or diameter?
- Use whichever you measured; pick the matching input mode so you do not double or halve twice.
- Does π use 3.14?
- Calculators use many decimal places of π for accuracy; homework may ask you to round the final area.
- What about a semicircle?
- Compute full circle area and divide by 2 (minus holes separately if any).