What This Calculator Does
This tool calculates the square footage of a circle — the area enclosed inside a round shape, expressed in square feet (ft²). It's useful for projects like circular patios, round rugs, garden beds, fountains, above-ground pools, and concrete pours where you need to know how much material to buy or how much surface you're covering.
How to Use It
Choose whether you are entering the diameter (the full width across the circle) or the radius (the distance from the center to the edge). Enter the measurement in feet, plus any leftover inches. The calculator converts everything to feet, computes the area, and also shows the diameter, circumference, square yards, and square meters for convenience.
The Formula Explained
The area of a circle is $$A = \pi \times r^{2}$$ where \(r\) is the radius in feet and \(\pi \approx 3.14159\). If you only know the diameter \(d\), first find the radius with \(r = d \div 2\), then square it and multiply by \(\pi\). Because the radius is measured in feet, the resulting area is automatically in square feet.
Worked Example
Suppose you have a circular patio with a diameter of 10 feet. The radius is \(10 \div 2 = 5\) feet. The area is $$A = \pi \times 5^{2} = \pi \times 25 \approx 78.54 \text{ square feet}$$ The circumference is \(2 \times \pi \times 5 \approx 31.42\) feet. To convert to square yards, divide by 9: \(78.54 \div 9 \approx 8.73 \text{ yd}^{2}\).
FAQ
What if I only know the radius? Just select "Radius" and enter it directly — no need to double it.
How do I convert square feet to square yards? Divide the square footage by 9, since one square yard equals 9 square feet.
Should I add extra for waste? For materials like sod, tile, or concrete, professionals often add 5–10% to the calculated area to cover cuts and waste.
