Area of a Circle Calculator
Enter a radius or diameter to instantly calculate a circle's area and circumference with step-by-step formulas.
Circle Dimensions
Unit label is optional — used only for display.
Results
Enter a value on the left to see results.
Radius
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Diameter
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Area (A = πr²)
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Circumference (C = 2πr)
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Formula Breakdown
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Summary
Enter a radius or diameter to instantly calculate a circle's area and circumference with step-by-step formulas.
How it works
- Choose whether you are entering a radius or a diameter.
- Type the value in the input field.
- The calculator applies A = πr² to find the area.
- Circumference is computed as C = 2πr.
- All results and intermediate steps display immediately.
- Use the precision slider to adjust decimal places shown.
Use cases
- Calculate material needed to fill or cover a circular surface.
- Determine the cross-sectional area of a pipe or cylinder.
- Solve geometry homework problems involving circles.
- Estimate lawn, garden bed, or pool surface area.
- Verify engineering or architectural circle measurements.
- Convert between radius, diameter, area, and circumference.
Frequently Asked Questions
Last updated: 2026-06-09 ·
Reviewed by Nham Vu