Square Footage Calculator
Calculate square footage for rectangles, L-shaped rooms, circles, triangles, trapezoids, borders and rings, with square yards, square meters, acres, waste and total cost.
How it works
rectangle = length × width · L-shape = length × width − cut-out corner · circle = π × (diameter ÷ 2)² · triangle = ½ × base × height, or Heron’s formula from three sides · trapezoid = (side 1 + side 2) ÷ 2 × height · border = outside rectangle − inside rectangle · square yards = sq ft ÷ 9 · m² = sq ft × 0.0929 · acres = sq ft ÷ 43,560 · cost = area × (1 + waste%) × price
Pick the shape that matches the space and enter its measurements in feet (or meters with the Metric switch). Rectangles multiply length by width. An L-shaped room is measured as the full outside rectangle minus the missing corner, which is often easier than splitting it in two. Circles use π times the radius squared; triangles use half the base times the height, or Heron’s formula when you only know the three sides. A border or ring — a path around a patio, a mulch ring around a tree — is the outside shape minus the inside one. The area is then given in square feet, square yards (÷ 9, the unit carpet is sold in), square meters and acres. Use “Number of identical areas” for repeated rooms, add or subtract other areas, and add a waste allowance before pricing materials. The price can be per square foot, per square yard or per square meter.
Worked example
A 12 × 10 ft room is 12 × 10 = 120 square feet, which is 13.33 square yards or 11.15 m². Flooring at $5 per square foot costs 120 × 5 = $600. With a 10% waste allowance you would buy 132 sq ft for $660. An L-shaped room measuring 20 × 15 ft overall with a 6 × 5 ft corner missing is 300 − 30 = 270 sq ft.
Frequently asked questions
How do I measure an irregular room?
Choose the closest shape here — the L-shape option covers most irregular rooms. For anything more complex, split it into rectangles and triangles, work out the largest piece, then put the others in “Other area to add” (or subtract pieces such as an island). Rounding each measurement up to the next half foot gives a small safety margin.
Should I add waste to a material order?
Yes — add 5–10% for straight flooring layouts and 10–15% for diagonal or herringbone patterns and rooms with many cuts. The waste allowance under More options adds it to the area and the cost. Buy everything from one lot so colors and dye batches match.
How do I find the square footage of a circle?
Measure the diameter (straight across through the center), halve it to get the radius, and multiply π (3.14159) by the radius squared. A 10 ft circle is 3.14159 × 5² = 78.54 sq ft.
What is the difference between square feet and linear feet?
Square feet measure area (length × width); linear feet measure a single dimension along a run, like trim or countertop edge. The perimeter result is in linear feet, which is what you need for baseboard or edging.
How many square feet are in a square yard, a square meter and an acre?
A square yard is 9 sq ft, a square meter is about 10.764 sq ft, and an acre is 43,560 sq ft. The calculator shows all of these for your area.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.