What is the formula for the area of a semicircle?

The area of a semicircle is A = (π × r²) / 2, where r is the radius. This is simply half the area of a full circle with the same radius.

What is the perimeter of a semicircle?

The perimeter (total boundary length) of a semicircle is P = π × r + 2r = r(π + 2), where r is the radius. It includes the curved arc (πr) plus the straight diameter (2r).

How do I calculate the area from the diameter?

If you know the diameter (d), the radius is r = d / 2. Substitute into the formula: A = (π × (d/2)²) / 2 = π × d² / 8.

What units does this calculator support?

You can enter measurements in millimeters, centimeters, meters, inches, or feet. Area is returned in the corresponding square unit (e.g., cm²) and perimeter in the linear unit (e.g., cm).

What is the difference between the arc length and the perimeter?

The arc length of a semicircle is just the curved part: πr. The perimeter (total boundary) also includes the straight diameter: πr + 2r. This calculator shows both values.

Is a semicircle half of a circle?

Yes. A semicircle is exactly one half of a circle, created by cutting the circle along a diameter. Its area is exactly half the area of the full circle.

Area of a Semicircle Calculator

Name: Area of a Semicircle Calculator
Availability: InStock
Author: Nham Vu

Enter a radius or diameter to instantly calculate the area and perimeter of a semicircle with step-by-step working.

Calculator Inputs

Input mode

Radius (r)

Unit

Area

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Perimeter

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Arc length (curved part only)

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Semicircle diagram

r = radius | d = diameter

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Summary