Semicircle Calculator

Work out semicircle instantly with clear inputs, formula shown and shareable results.

About Semicircle Calculator

A semicircle is half a disc, so its area is πr²/2. Its boundary is the half-circumference πr plus the straight diameter 2r, and its centroid sits 4r/(3π) above the diameter.

Formulas

Area

A = πr² / 2

Perimeter

P = πr + 2r

Centroid

ȳ = 4r / (3π)

Worked example

With the default values below, Semicircle Calculator returns Area of one semicircle of 56.5487. Change any input above and every figure here is recalculated in your browser.

Inputs used

Radiusminimum 0: 6
Number of semicirclesminimum 1: 1

Results

Area of one semicircle: 56.5487
Perimeter (arc + diameter): 30.8496
Centroid height above the diameter: 2.5465
Combined area: 56.5487

Step by step

1Values used
2Area
3Perimeter
4Centroid
5Area of one semicircle= 56.5487
6Perimeter (arc + diameter)= 30.8496
7Centroid height above the diameter= 2.5465
8Combined area= 56.5487

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is the perimeter just half the circle's?

No. Half the circumference is only the curved part; you must add the diameter that closes the shape.

Where is the centroid?

On the axis of symmetry, 4r/(3π) ≈ 0.4244r above the flat edge — not at r/2.