How it works

A semicircle is half of a full circle. Enter the radius to get the area, the curved arc length, and the total perimeter (arc plus diameter). Handy for circle geometry homework and exam-style questions.

The Formula

Area:
A = πr² ÷ 2 Curved length (half circumference):
L = πr Perimeter (arc + diameter):
P = πr + 2r

Worked Example

1. Worked example

   Radius r = 6 cm Area = π × 6² ÷ 2 = 18π ≈ 56.55 cm² Curved length = π × 6 ≈ 18.85 cm Perimeter = 18.85 + 12 ≈ 30.85 cm

Tips, Assumptions & Limitations

• The diameter is always twice the radius: d = 2r.
• Perimeter includes the straight diameter, not just the curved part.
• Area uses the same πr² formula as a full circle, then divide by 2.