Square footage calculator

Square footage is length multiplied by width, and almost every material estimate starts with it: flooring, paint, insulation, sod, tile adhesive. This calculator returns the area for one space or several identical ones, with an optional deduction, along with square yards for materials sold that way and the perimeter for anything you buy by the linear foot.

Length (ft)

Width (ft)

Number of identical areas (count)

Use 4 for four bedrooms of the same size.

Deduct (sq ft)

Stairs, a chimney breast, or any area not being covered.

Total area

120.0sq ft

Per area 120.0 sq ftSquare yards 13.33 yd²Perimeter of one 44.0 ft

Rectangles only. Curved walls, angled rooms and multi-level spaces need to be broken into shapes and summed, and the total will differ slightly from a measured plan.

Measure in feet and inches and convert before entering — a room that is 12 ft 6 in wide is 12.5, not 12.5 inches or 12 foot 5. Take each dimension at two or three points and use the largest, because rooms are rarely square and the material has to cover the widest part.

For an L-shaped room, split it into two rectangles and run each one separately; the same applies to a room with an alcove. Adding a deduction is useful where something occupies the space permanently, such as a chimney breast or a stair well, but it should not be used to subtract furniture or a kitchen island — flooring goes underneath them.

How the calculation works

Area = length (ft) × width (ft). For several identical areas, multiply by the count. Total = (area × count) − deduction. Square yards = total ÷ 9, because a square yard is 3 ft × 3 ft. Perimeter = 2 × (length + width).

• Every space measured is a rectangle of the dimensions entered; L-shaped and irregular rooms should be split and summed.
• Dimensions are interior face-to-face measurements in feet, taken at the widest point.
• The deduction is a floor area removed once, not per area, which is the usual case for a chimney breast or a stair opening.
• No allowance is made for waste or overlap; add 5-10% when ordering flooring, and more for a diagonal layout.

Sources: 1 square yard = 9 square feet; Area of a rectangle = length × width; triangle = ½ × base × height

Worked examples

Questions

How do I calculate square footage of an irregular room?

Split it into rectangles, calculate each, and add them. A room with an alcove is two rectangles; an L-shaped room is two rectangles sharing a corner. Triangles are half of a rectangle with the same base and height.

How many square feet is a 12 × 12 room?

144 sq ft, or 16 sq yd. Add 10% when ordering flooring, so 158 sq ft.

How do I convert square feet to square yards?

Divide by 9. A 120 sq ft room is 13.33 sq yd, which is the unit carpet is usually sold in.

Should I measure in inches or feet?

Measure in feet and inches, then convert to a decimal in feet before entering: 12 ft 6 in is 12.5. Multiplying inches and dividing later is where most square footage errors come from.

Does square footage include closets?

For flooring and paint, yes — closets have floors and often walls. For an appraisal or a listing, the rules differ and usually exclude closets that are not heated; this calculator measures the space, not the legal area.

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Written and maintained by Sam Winters. Last updated 2026-11-04. Every figure is computed in your browser; nothing you enter is sent anywhere. Found an error? Tell me — accuracy reports get fixed first.