Square Foot Calculator Half Circle
Calculate the square footage of a half circle (semicircle). Enter the radius or diameter to get the area in square feet.
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.