Square Footage of a Circle

Area of a circular room, patio or pad from its diameter, with the radius step shown rather than folded into one formula.

With diameter 12 ft, number of identical areas 1, waste factor 10 percent, price per square foot 0 usd, square footage comes to 124.4 sq ft — area to order. It is reached in 9 steps, the last of which is subtotal * (1 + waste / 100), and each one is printed on the page with its numbers filled in. The formula is the one published by ANSI Z765 residential square footage measurement standard, not an approximation fitted to it.

Formula and sources checked 16 August 2026 · How we check

What to measure

ShapeDiameterNumber of identical areasWaste factorpercent10% for straight-lay, 15% for diagonal, 20% for herringbone.Price per square footusdLeave at zero to skip the cost. Flooring is priced per square foot and sold by the carton.

Area to order

124.4 sq ft

11.6 square metres

The three sides close into a triangle: heron > 0 ? 1 : 01
Area of the openings: openings * opening_w * opening_h30 sq ft
Area per shape: 113.097 sq ft
Total area: area * rooms113.097 sq ft
Area to order: subtotal * (1 + waste / 100)124.407 sq ft
Same area in square meters: total / 10.763911.558 sq m
Same area in square yards: total / 913.823 sq yd
Same area in acres: total / 435600.003 acres
Material at that price: total * price$0

The formula

The three sides close into a triangleheron > 0 ? 1 : 0
Area of the openingsopenings * opening_w * opening_h
Area per shapeshape_rect * (length * width) + shape_wall * max(0, length * width - openings_area) + shape_border * ((length + 2 * border_width) * (width + 2 * border_width) - length * width) + shape_trapezoid * ((top_width + bottom_width) / 2 * trap_height) + shape_circle * (pi * pow(diameter / 2, 2)) + shape_annulus * (pi * (pow(diameter / 2, 2) - pow(min(inner_diameter, diameter) / 2, 2))) + shape_triangle * (base * tri_height / 2) + shape_triangle_sides * sqrt(heron)
Total areaarea * rooms
Area to ordersubtotal * (1 + waste / 100)
Same area in square meterstotal / 10.7639
Same area in square yardstotal / 9
Same area in acrestotal / 43560
Material at that pricetotal * price

Formula from ANSI Z765 residential square footage measurement standard, NIST Office of Weights and Measures.

The same calculator, other cases

Square Footage of a TriangleArea of a triangular space from its base and height — the shape a gable end or a corner of a room makes.

Undecided? The Square Footage Calculator carries every case behind one control.

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