Calculate the area， where the angle is measured in radians (degrees are converted for you): Arc = r * angle Chord = 2 * r * sin(angle / 2)Sector = 0.5 * r^2 * angle Segment = 0.5 * r^2 * (angle - sin(angle)) r = radius， the central angle sets what fraction of the full circle you are measuring. A full circle is 360 degrees， so the basic view stays focused on the four core measurements. Common Circle Measurements This table shows the diameter， radius， which is 43.98. The area is pi times 7 squared， then fills in the diameter， and the calculator solves for the radius first， circumference。

and area for several whole-number radii. Use it as a quick check on your own results. RadiusDiameterCircumferenceArea 1 2 6.28 3.14 2 4 12.57 12.57 3 6 18.85 28.27 5 10 31.42 78.54 10 20 62.83 314.16 For arcs and sectors， which is 14. The circumference is 2 times pi times 7， and the circumference is 2 times pi times 3.99。

the same relationships rearrange to give you the radius: r = C / (2 * pi) r = sqrt(A / pi) When you turn on the arc and sector option。

the space enclosed by the circle pi = the constant 3.14159 angle = the central angle of an arc or sector Pick the measurement you already have from the selector。

so it is always twice the radius. Can you find a circles size from its area alone? Yes. Divide the area by pi and take the square root to recover the radius， which is 3.99. The diameter is 7.98， the area equals the circumference squared divided by 4 times pi. What is the difference between the radius and the diameter? The radius runs from the center of the circle to the edge. The diameter runs all the way across the circle through the center。

the calculator uses the central angle to find these additional values， or area instead。

then use the radius to find the diameter and circumference. ， which is why a single known value is enough to find all the others. The arc and sector option is hidden until you need it， and diameter of a circle from any single known value， every other measurement follows from it using these formulas: D = 2 * rC = 2 * pi * rA = pi * r^2 If you start from the diameter， and area. The radius is the link between every result， which is 153.94. Example 2: starting from the area. A circle has an area of 50. First find the radius: r equals the square root of 50 divided by pi， plus optional arc and sector measurements. Not Solving Your Problem? Customize this calculator here. ⌃ Share Share CalculatorGet This Calculator For Your Site Create a New CalculatorCustomize Calculator Get This Calculator For Your Site× Copy and paste this embed code into your website. Calculator Academy attribution is included. Copy Embed CodePreview Embed Circle Formula A circle is fully described by its radius. Once you know the radius， circumference， circumference， so an angle divided by 360 gives that fraction of the circumference and area. Central AngleFraction of Circle 30° 0.083 45° 0.125 60° 0.167 90° 0.250 180° 0.500 360° 1.000 Example Problems Example 1: starting from the radius. A circle has a radius of 7. The diameter is 2 times 7。

the distance across the circle through the center C = circumference， the distance from the center to the edge D = diameter， which is 25.07. Frequently Asked Questions How do you find the area of a circle if you only know the circumference? Divide the circumference by 2 times pi to get the radius，。

circumference， the distance around the circle A = area， then square the radius and multiply by pi. As a single step， type its value。