Calculate area, circumference, diameter, and radius — enter any one measurement.
Enter any one measurement — all others are calculated.
All circle measurements relate through the radius. Knowing any one measurement (r, d, C, or A) lets you calculate all others. Circumference = π × diameter — π is the ratio of every circle's circumference to its diameter. Arc length = (angle/360°) × 2πr.
Area = π × r² where r is the radius. If you know diameter d: Area = π × (d/2)² = πd²/4. For circumference C: Area = C²/(4π). Example: circle with radius 6 has area = π × 36 ≈ 113.1 square units.
π ≈ 3.14159265… is the ratio of any circle's circumference to its diameter. It is irrational (infinite, non-repeating decimal) and transcendental. It appears throughout mathematics, physics, engineering, and statistics beyond just circles.
Calculate the area of any shape — circle, triangle, rectangle, and more.
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Solve a² + b² = c² for any unknown side of a right triangle.