Calculate the area of a half-circle from either its radius or its diameter.
Last updated: June 2026 | By Patchworkr Team
Enter a real number.
The semicircle area formula is half the area of a full circle.
If you enter a diameter, the calculator halves it first to recover the radius.
Select radius or diameter, enter a positive value, and read the live semicircle area.
With diameter 120, the radius is 60 and the area is 5654.866778.
That is exactly half of the full circle area 11309.733553.
The live result means the calculator updates as soon as the radius or diameter changes.
Blank, malformed, zero, and negative inputs are rejected explicitly so the result cannot silently become zero.