Circumference Calculator
Calculate the circumference, area, radius, and diameter of a circle instantly. Enter any known value to find the rest with precision.
Circle Properties Calculator
Find circumference, area, radius, and diameter
Enter the value of the circle property you know
Select which property you are providing
Select the unit of measurement
Circle Properties
Calculated dimensions and formulas
Enter a value and select the input type, then click Calculate to see all circle properties.
Circle Formulas
Mathematical formulas used to calculate circle properties.
| Property | Formula (from Radius) | Formula (from Diameter) | Formula (from Area) |
|---|---|---|---|
| Circumference (C) | 2πr | πd | 2√(πA) |
| Area (A) | πr² | π(d/2)² | A |
| Radius (r) | r | d/2 | √(A/π) |
| Diameter (d) | 2r | d | 2√(A/π) |
Circle Geometry FAQ
Everything you need to know about calculating circle properties.
The formula for the circumference of a circle is C = 2πr or C = πd, where C is the circumference, r is the radius, d is the diameter, and π (Pi) is approximately 3.14159. The circumference is the total distance around the outside of the circle.
To find the circumference from the area, first find the radius using the formula r = √(A/π), where A is the area. Then, calculate the circumference using C = 2πr. Alternatively, you can use the direct formula C = 2√(πA). For example, if the area is 50 square units, the radius is √(50/3.14159) ≈ 3.99, and the circumference is 2 × 3.14159 × 3.99 ≈ 25.06 units.
The radius is the distance from the center of the circle to any point on its edge. The diameter is the distance across the circle passing through the center. The diameter is exactly twice the length of the radius (d = 2r). Conversely, the radius is half the diameter (r = d/2).
Pi (π) is a mathematical constant representing the ratio of a circle’s circumference to its diameter. It is an irrational number, meaning it cannot be expressed as a simple fraction and its decimal representation never ends or repeats. Its value is approximately 3.14159, though it is often approximated as 3.14 or 22/7 for basic calculations.
The area of a circle is calculated using the formula A = πr², where A is the area and r is the radius. If you know the diameter instead, you can use A = π(d/2)². For example, a circle with a radius of 5 units has an area of 3.14159 × 5² = 78.54 square units.
Yes. If you know the diameter, use C = πd. If you know the area, use C = 2√(πA). You can also calculate it if you know the arc length and the central angle, though this is less common for basic circle calculations.