Math

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Semicircle Area Calculator.

Calculate the area and dimensions of a semicircle.

On-device calculationNo signup
01

Set your values

Results update as you type.

Area: 39.269908

Area

0.000000
Diameter: 10

Diameter

0.000000
Arc length: 15.707963

Arc length

0.000000

Results update automatically as you type.

Use Cases

Geometry homework and exam prep

Quickly verify your manual calculations for semicircle area, arc length, perimeter, and diameter when solving geometry problems.

Example: Check the area of a semicircle with radius 5 cm.

Designing arches and curved structures

Get accurate dimensions for semicircular elements in architecture, landscaping, or crafting, such as archways, garden beds, or window tops.

Example: Find the perimeter of a semicircular garden bed with radius 2 meters.

Frequently Asked Questions

How do I calculate the area of a semicircle?
Enter the radius of the semicircle into the calculator. The area is computed as half the area of a full circle: (π × radius²) ÷ 2. The calculator also provides the arc length, perimeter, and diameter based on the radius you enter.
What is the formula for the perimeter of a semicircle?
The perimeter of a semicircle is the sum of the arc length (half the circumference) and the diameter. The formula is: perimeter = (π × radius) + (2 × radius). This calculator uses your radius input to compute this automatically.
Can I use this calculator if I only know the diameter?
No, this calculator requires the radius. If you know the diameter, simply divide it by 2 to get the radius, then enter that value. The calculator will then compute the area and other dimensions.

Tips & Common Mistakes

Tips

  • Ensure the radius is measured in the same unit you want for the results (e.g., meters, feet, inches).
  • If you have the diameter, divide it by 2 to get the radius before entering it.
  • Use the arc length result when you need the length of the curved edge alone, not the full perimeter.
  • Double-check that you are entering the radius, not the diameter, to avoid incorrect area calculations.

Common Mistakes to Avoid

  • Entering the diameter instead of the radius, which gives an area four times larger than the correct value.
  • Forgetting that the perimeter includes the straight diameter, not just the curved arc.
  • Using the full circle area formula without dividing by 2, resulting in double the actual semicircle area.

Last updated: August 13, 2026