Choose the angle unit, enter a positive radius, and keep the angle within the valid sector range.

1. Select degrees or radians.
2. Enter a radius greater than 0.
3. Enter an angle from 0 up to the full circle limit.

With radius 10 and angle 72 degrees, the sector area is 62.831853.

That is exactly one-fifth of the full circle area, which is 314.159265.

The calculator rejects angles outside the full sector range so it cannot silently compute a wrapped or impossible sector.

The result is live, so changing the unit or input immediately updates the geometry without needing a separate calculate button.