Segment Area Calculator

Segment Area Calculator

Calculate the area of a circular segment

How To Calculate Segment Area

Step 1: Determine the Radius

Measure the distance from the center of the circle to any point on the circumference.

Why: Radius scales all area calculations quadratically; accuracy here is critical.

Step 2: Measure the Central Angle

Find the angle subtended at the center by the chord bounding the segment.

Why: The angle determines the size of the sector that includes the segment.

Step 3: Convert to Radians if Needed

If angle is in degrees, convert using θ(rad) = θ(°) × π / 180.

Why: The segment formula requires radians; degrees would produce incorrect results.

Step 4: Calculate Using the Segment Formula

Apply A = ½ × r² × (θ - sin(θ)) where θ is in radians.

Why: This formula directly subtracts the triangular part from the sector, isolating the curved segment.

Step 5: Verify Reasonableness

Confirm the segment area is less than the corresponding sector area.

Why: A segment (curved region) must be smaller than its containing sector.

Detailed Example

Scenario: A circular segment has radius 6 m and central angle 90°. Find the segment area.
Step 1 - Determine Radius: r = 6 m (distance from center to circumference).
Step 2 - Measure Angle: θ = 90° (central angle at circle center).
Step 3 - Convert to Radians: θ = 90 × π/180 = π/2 ≈ 1.571 rad.
Step 4 - Apply Formula: A = ½ × 6² × (π/2 - sin(π/2)) = ½ × 36 × (1.571 - 1) = 18 × 0.571 ≈ 10.29 m².
Step 5 - Verify: Sector area = ½ × 36 × 1.571 = 28.27 m². Segment (10.29) < Sector (28.27) ✓
Verification: sin(π/2) = 1, so π/2 - 1 ≈ 0.571 is correct.
Result: The circular segment area is approximately 10.29 m².
Interpretation: The segment is the "crescent" region between the chord and arc; it's always smaller than the sector containing it.

Formula Information

A circular segment is the region bounded by a chord and the arc it intercepts. Its area is calculated as:

A = ½ × r² × (θ - sin(θ))

Where θ is the central angle in radians.

Related Tools