Square Inches of a Circle Calculator — Circle Area in in²
Find the area of any circle in square inches by entering its diameter. The calculator uses the exact formula A = π × r² and also shows the result in square feet and square centimetres.
in
Area = π × (diameter ÷ 2)²
- 1
Radius
10 ÷ 2 = 5 - 2
Area
π × 5² = 78.5398Area = π × radius², where π ≈ 3.14159.
How does this calculator work?
The area of a circle in square inches is A = π × (d/2)², where d is the diameter in inches. For a 10-inch diameter circle: A = π × 5² ≈ 78.54 in². Divide by 144 to convert to square feet, or multiply by 6.4516 for square centimetres.
Formula
How this is calculated
The area enclosed by a circle is given by A = π × r², where r is the radius (half the diameter) and π is the mathematical constant ≈ 3.14159265. Diameter is used as the input because it is easier to measure — clamp a ruler across the widest point of a circular object and you have the diameter directly, without having to locate the exact centre first.
To convert the result to other area units: divide by 144 to get square feet (since 1 ft² = 144 in²), or multiply by 6.4516 to get square centimetres (since 1 in² = 6.4516 cm²). The circumference is also shown for reference: C = π × d.
The formula assumes a perfect flat circle. For a sphere, cylinder cap or other 3-D circular surface you would need a different formula. The calculation uses JavaScript's Math.PI (accurate to 15–16 significant figures), so rounding is negligible for any practical measurement.
Frequently asked questions
Use A = π × r², where r is the radius in inches (half the diameter). Or enter the diameter in this calculator — it divides by 2 and applies the formula automatically. For example, a circle with a 10-inch diameter has r = 5 in and area = π × 5² ≈ 78.54 in².
Divide the square-inch area by 144 (since 1 ft² = 144 in²). For example, 78.54 in² ÷ 144 ≈ 0.5454 ft².
Diameter is easier to measure directly — you can place a ruler across the widest point of a circular object. The calculator halves it to get the radius before applying A = π × r².
Also known as
TG we-Calculate Editorial Team. (2026). Square Inches of a Circle Calculator — Circle Area in in² [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/square-inches-of-a-circle-calculator
TG we-Calculate Editorial Team. "Square Inches of a Circle Calculator — Circle Area in in²." TG we-Calculate. 2026. https://we-calculate.com/calculator/square-inches-of-a-circle-calculator.
TG we-Calculate Editorial Team, "Square Inches of a Circle Calculator — Circle Area in in²," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/square-inches-of-a-circle-calculator
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