Circle Area Calculator
Calculate the area of a circle from its radius or diameter, with the circumference.
Your inputs
Results
Area
78.539816 m²
- Radius
- 5 m
- Circumference
- 31.415927 m
✓Exact calculation — rounded only for display
What this calculator does
Circle areas come up in tables, pipes, pizzas and garden beds.
Formula and method
Area = π r² = π d² ÷ 4
Worked example
Calculated by this tool with its default inputs:
Inputs
- Length unit: Metres
- I know the: Radius
- Radius or diameter: 5
Results
- Area: 78.539816 m²
- Radius: 5 m
- Circumference: 31.415927 m
How to read the results
Doubling the diameter quadruples the area.
Assumptions and limitations
- Use one length unit consistently; areas are in square units and volumes in cubic units of that length.
Quantities and costs are planning estimates. Add sensible allowances, and check with suppliers, carriers or professionals before buying, shipping or building.
Questions
Is a 16-inch pizza twice a 12-inch?
Its area is (16/12)² ≈ 1.78 times larger.
Methodology and verification
- Result type
- Exact mathematical calculation (rounded only for display)
- Formula version
- 1.0
- Automated verification
- 3 reference and validation test cases, checked against independently computed values. The site cannot be built if any of them fail.
- Editorial review
- Awaiting human editorial review. The explanation was drafted with AI assistance; the formula and examples are verified by the automated tests above.
Privacy
Everything you enter is calculated in this browser and is not sent to Numerith or anyone else. Inputs are added to a share link only if you choose to include them. Privacy policy