Enter any one measurement — radius, diameter, circumference, or area — and instantly get all four circle properties.
A circle calculator finds the radius, diameter, circumference, and area of a circle from just one known measurement. Enter any single value — radius, diameter, circumference, or area — and the calculator instantly derives the other three using standard geometric formulas.
Let r be the radius and π (pi) ≈ 3.14159:
Suppose a circular table has a radius of 7 cm. The diameter is 2 × 7 = 14 cm. The circumference is 2 × π × 7 ≈ 43.98 cm. The area is π × 7² ≈ 153.94 cm². Enter "7" as the radius above to confirm this instantly.
Circle calculations are useful for sizing round tables, pipes, wheels, garden beds, pizza comparisons, and any project involving circular shapes in construction, crafting, or engineering.
Area = π × radius²; Circumference = 2 × π × radius. Enter any one value (radius, diameter, area, or circumference) to get the rest.
The diameter is the full distance across the circle through its center; the radius is half of that, from the center to the edge.
π (pi) represents the fixed ratio between a circle's circumference and its diameter — approximately 3.14159 — the same for every circle regardless of size.