Circle Calculator
Calculate all circle properties from any known value. Enter radius, diameter, circumference, or area to compute the rest.
Enter Radius
Unit:
Radius
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Diameter
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Circumference
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Area
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Additional Calculations
Arc Length
Arc Length
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Sector Area
Sector Area
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Segment Area
Segment Area
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Circle Formulas
Diameter from Radius
d = 2r
Diameter is twice the radius
Circumference
C = 2(pi)r = (pi)d
Perimeter of the circle
Area
A = (pi)r(sq)
Space enclosed by the circle
Arc Length
L = (theta/360) x 2(pi)r
Length of arc for angle theta
Sector Area
A = (theta/360) x (pi)r(sq)
Area of pie-slice section
Segment Area
A = (r(sq)/2)(theta - sin(theta))
Area between chord and arc
Frequently Asked Questions
How do I find the circumference of a circle?
The circumference of a circle can be calculated using C = 2 x pi x r (where r is the radius) or C = pi x d (where d is the diameter). Simply multiply pi (approximately 3.14159) by the diameter, or multiply 2 x pi by the radius.
What is the formula for the area of a circle?
The area of a circle is calculated using A = pi x r squared, where r is the radius. If you know the diameter, first divide it by 2 to get the radius, then square the radius and multiply by pi.
How do I calculate arc length?
Arc length is calculated using the formula: Arc Length = (angle/360) x 2 x pi x r, where the angle is in degrees and r is the radius. This gives you the length of the curved portion of the circle.
What is the difference between a sector and a segment?
A sector is a "pie slice" of the circle bounded by two radii and an arc. A segment is the region between a chord (straight line connecting two points on the circle) and the arc it cuts off. The sector includes the triangular portion to the center, while the segment does not.