Square Foot Calculator Half Circle
Find semicircle square footage instantly. Enter radius or diameter — get area in sq ft, m², sq yd, and acres. Free for patios and arches.
Half Circle (Semicircle) Calculator
Enter the radius or diameter of the half circle.
Exactly half the area of a full circle.
How to Calculate Square Footage of a Half Circle
A half circle (semicircle) is exactly half of a full circle, commonly found in arched windows, semicircular patios, half-round gardens, bay window areas, and driveway turnarounds. The flat edge is the diameter.
Half Circle Area Formula
This is simply half the area of a full circle. Measure the straight edge (diameter) and divide by 2 to get the radius.
Step-by-Step Instructions
- Measure the diameter — the straight edge of the semicircle (the flat side).
- Divide by 2 to get the radius.
- Square the radius and multiply by π (3.14159).
- Divide by 2 to get the half-circle area.
Worked Examples
A semicircular window has a diameter of 6 feet (radius = 3 feet).
½ × π × 3² = ½ × 28.27 = 14.14 square feet
A semicircular driveway turnaround has a diameter of 20 feet (radius = 10 feet).
½ × π × 10² = ½ × 314.16 = 157.08 square feet
Common Semicircle Sizes
| Diameter | Radius | Area (sq ft) |
|---|---|---|
| 4 ft | 2 ft | 6.28 sq ft |
| 8 ft | 4 ft | 25.13 sq ft |
| 12 ft | 6 ft | 56.55 sq ft |
| 16 ft | 8 ft | 100.53 sq ft |
| 20 ft | 10 ft | 157.08 sq ft |
Common Uses
- Arched window & doorway areas — glass, trim, and covering calculations
- Semicircular patios — pavers, concrete, or gravel area estimation
- Half-round garden beds — soil, mulch, and planting calculations
- Bay window floor areas — flooring beneath curved window bays
- Driveway turnarounds — asphalt or concrete pouring area
Frequently Asked Questions
How do I calculate the area of a half circle? +
Use the formula Area = ½ × π × r². Measure the diameter (the straight edge), divide by 2 to get the radius, then calculate half the area of a full circle.
What is the square footage of a 6-foot diameter half circle? +
Radius = 3 ft. Area = ½ × π × 3² = ½ × 28.27 = 14.14 square feet.
Where do semicircular shapes appear in buildings? +
Arched windows, doorway transoms, bay window floor areas, semicircular patios, half-round garden beds, and driveway turnarounds.
Can I use radius or diameter in this calculator? +
Yes, enter either one. If you enter the diameter, the calculator automatically divides by 2 to find the radius before calculating.