Circle Calculator
Enter a radius, diameter, circumference, or area to find every circle measurement, plus arcs, sectors, chords, and segments.
Radius
10.000 cm
r = 10.000
Diameter
20.000 cm
d = 2r = 20.000
Circumference
62.832 cm
C = 2πr = 62.832
Area
314.159 cm²
A = πr² = 314.159
Unit Conversions
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What is Circle Calculator?
A circle calculator helps you find all properties of circles using any single measurement. Whether you know the radius, diameter, circumference, or area, this calculator can determine all other measurements using fundamental circle formulas based on π (pi).
Circle Properties
- Radius: Distance from center to any point on the circle
- Diameter: Distance across the circle through the center (2 × radius)
- Circumference: Distance around the circle (2π × radius)
- Area: Space inside the circle (π × radius²)
Advanced Properties
- Arc Length: Distance along the circumference for a given central angle
- Sector Area: Area of a slice of the circle for a given central angle
- Chord Length: Straight-line distance between two points on the circle
- Segment Area: Area between a chord and the arc
Key Formulas
- Circumference: C = 2πr = πd
- Area: A = πr²
- Arc Length: L = (θ/360°) × 2πr
- Sector Area: A = (θ/360°) × πr²
Worked Circle Examples
From radius: A radius of 5 cm gives a diameter of 10 cm, circumference of about 31.416 cm, and area of about 78.540 cm².
From diameter: A diameter of 12 in gives a radius of 6 in and circumference of about 37.699 in.
Unit reminder: Linear results use the selected length unit; area and sector results use its corresponding square unit.