Square Foot Calculator Circle
Calculate the square footage of a circle. Enter the radius or diameter to get the area in square feet using π × r².
Circle Area Calculator
Enter the radius or diameter of the circular area. Only one is needed.
Radius = half the diameter.
π (pi) ≈ 3.14159
How to Calculate Square Footage of a Circle
Circles appear in round rooms, pools, patios, fire pits, round gardens, circular driveways, trampolines, and round rugs. The area of a circle depends on its radius — the distance from the center to the edge.
Circle Area Formula
Where π (pi) ≈ 3.14159. The radius (r) is half the diameter. If you know the diameter, divide it by 2 to get the radius, then square it and multiply by π.
Step-by-Step Instructions
- Measure the diameter — the distance across the widest point of the circle, passing through the center.
- Divide by 2 to find the radius.
- Square the radius (multiply it by itself).
- Multiply by π (3.14159) to get the area in square feet.
Worked Examples
A circular patio has a diameter of 16 feet (radius = 8 feet).
π × 8² = 3.14159 × 64 = 201.06 square feet
A round pool has a diameter of 24 feet (radius = 12 feet).
π × 12² = 3.14159 × 144 = 452.39 square feet
Common Circular Area Sizes
| Diameter | Radius | Area (sq ft) |
|---|---|---|
| 6 ft | 3 ft | 28.27 sq ft |
| 10 ft | 5 ft | 78.54 sq ft |
| 15 ft | 7.5 ft | 176.71 sq ft |
| 20 ft | 10 ft | 314.16 sq ft |
| 24 ft | 12 ft | 452.39 sq ft |
| 30 ft | 15 ft | 706.86 sq ft |
Practical Applications
- Pool covers and decking — calculate the area around a round pool for decking or safety covers
- Circular patios — area needed for pavers, concrete, or gravel
- Fire pit zones — determine the clearance area around a fire pit
- Round rugs — choose the right rug size for a circular dining area
- Garden beds — calculate soil, mulch, or sod needed for round plantings
- Trampolines — determine the footprint and safety zone
Circle vs. Square Comparison
A circle inscribed in a square (touching all 4 sides) covers approximately 78.5% of the square's area. This means a 10-foot diameter circle (78.54 sq ft) fits inside a 10 × 10 square (100 sq ft), with 21.46 sq ft of unused corner space.
Frequently Asked Questions
How do I calculate the area of a circle in square feet? +
Use the formula Area = π × r², where r is the radius (half the diameter). Measure the diameter across the widest point, divide by 2, square it, and multiply by 3.14159.
What is the square footage of a 10-foot diameter circle? +
Radius = 5 ft. Area = π × 5² = π × 25 = 78.54 square feet. This is about 7.30 square meters.
How do I measure the radius of a circular area? +
Measure the diameter (the widest distance straight across the circle through the center) and divide by 2. Alternatively, measure from the center point to any edge.
How much area does a round pool cover? +
Measure the diameter of the pool, divide by 2 to get the radius, then calculate π × r². A 15-foot diameter pool covers about 176.7 square feet.
Can I enter the diameter instead of the radius? +
Yes! This calculator accepts either radius or diameter. If you enter both, the radius value takes priority. If you only enter diameter, the calculator automatically divides by 2.