Case 1
- Radius
- 5
39.269908
Open with these valuesSemicircle Area Calculator
39.269908units²
Result: 39.269908 units²Half a circle, so half the area: πr² ÷ 2. Radius 5 gives 39.27 square units. Careful with the perimeter — it is not half the circumference, because a half circle also has the straight edge across the middle, adding 2r.
Worked examples
How it's calculated
A = π × r² ÷ 2
- StepMeasure the radius — half the straight edge.
- StepEnter it in any length unit.
- ResultRead the area in the square of that unit.
Reference table
| Radius | Exact | Area |
|---|---|---|
| 1 | π ÷ 2 | 1.570796 |
| 2.5 | 3.125π | 9.817477 |
| 5 | 12.5π | 39.269908 |
| 7 | 24.5π | 76.969020 |
| 10 | 50π | 157.079633 |
Questions
How do you calculate the area of a semicircle?
Square the radius, multiply by π and halve it. A radius of 5 gives 12.5π, about 39.27 square units.
What is the perimeter of a semicircle?
The curved half, πr, plus the straight edge, 2r — together r(π + 2). For radius 5 that is 25.71, not the 15.71 of the arc alone.
I measured the flat edge, not the radius.
That edge is the diameter, so halve it. A half circle 10 across has a radius of 5.
Sources and last check
Information, not professional advice.