Arc of a Circle

A connected section of the circumference of a circle.

Arcs are measured in two ways: as the measure of the central angle, or as the length of the arc itself.

Measurement by central angle (degrees)

The red arc (minor arc) measures 120°.

The blue arc (major arc) measures 240°.

Formula: s = rθ s = arc length r = radius of the circle θ = measure of the central angle in radians

Red arc: r = 2 and θ = 2π/3, so s = 4π/3

Blue arc: r = 2 and θ = 4π/3, so s = 8π/3

See also

Arc length of a curve