Area Calculator FAQ
What is the formula for the area of a circle?
The standard formula is A = pi r^2, where r is the radius. If you know the diameter, use A = pi d^2 / 4. If you know the circumference, use A = C^2 / (4pi).
How do you calculate circle area from the diameter?
Use A = pi d^2 / 4, or divide the diameter by 2 to get the radius and then apply A = pi r^2.
How do you find the radius from the area?
Rearrange the formula to r = sqrt(A / pi). The calculator uses this reverse formula when the area is the known input.
How do you calculate circle area from the circumference?
Use A = C^2 / (4pi). You can also find the radius from r = C / (2pi) first and then apply A = pi r^2.
What is the area of a semicircle or quarter circle?
A semicircle has area pi r^2 / 2, and a quarter circle has area pi r^2 / 4.
When is an area of a circle calculator useful?
It is useful for geometry, round tables, circular rugs, pizza size comparisons, pipe cross-sections, circular plots, pools, and any practical problem involving a round area.
