Math
Sector Area Calculator
Use this sector area calculator for slices of circles, pie-chart pieces, and geometry homework.
Sector area
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- Full circle area
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- Circle fraction
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the sector area calculator solves
Use this sector area calculator for slices of circles, pie-chart pieces, and geometry homework.
Formula
How to use it
- Enter radius.
- Enter central angle in degrees.
- Read the matching fraction of the full circle.
How to read the answer
Sector area is the same fraction of circle area as the central angle is of 360 degrees.
Common mistakes and edge cases
- Use degrees here, not radians.
- Do not use diameter as radius.
- Angles above 360 are not a single standard sector.
Worked examples
Sixty-degree sector
Sector area
33.5103
Semicircle
Sector area
39.2699
Frequently asked questions
How is sector area different from arc length?+
Sector area measures the slice's surface area; arc length measures only the curved edge.
Can the angle be zero?+
Yes, but the area is zero.
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Last updated: May 15, 2026