How do I calculate square footage?

Multiply length by width for a rectangle. A 12 ft by 10 ft room is 120 square feet; in metric, a 3.6 m by 3 m room is 10.8 m². For a circle, it is π times the radius squared — or use the diameter option here and let the tool do it. For an L-shaped room, split it into rectangles, work out each, and add them together.

How do I convert square feet to square metres?

Multiply square feet by 0.0929, or divide by 10.764. This tool shows both at once, so a 120 sq ft room reads as about 11.15 m² without you touching a conversion. The factor is just the square of the foot-to-metre ratio (0.3048² = 0.0929).

Do I subtract doors and windows?

It depends what the area is for. For flooring, work with the full floor area. For wall paint or drywall, subtract large openings if you want a tighter number, though many people leave them in as built-in waste. This tool gives you the gross area; subtract openings yourself where it matters.

How much extra should I add for waste?

Square footage itself is just the measurement, so this tool does not add waste — it gives the true area. Add the waste on the material tool instead: flooring, tile and drywall calculators apply a waste factor to the area you bring them.

Square footage calculator

This is the plain area of the shape you enter. It does not deduct openings or add waste — bring the area to a material tool for that, and measure twice before you order anything from it.

Pick a shape, enter the dimensions, and you get the area in square feet and square metres at the same time. A rectangle is length × width; a circle is π × radius². The "how many" field totals several identical areas in one go.

Exemple détaillé

A bedroom 12 ft × 10 ft is 12 × 10 = 120 square feet. To read that in metric, multiply by 0.0929: 120 × 0.0929 ≈ 11.15 m². Two identical bedrooms would be 240 sq ft. A round patio 10 ft across is π × 5² ≈ 78.5 sq ft.

In metric: a bedroom 3.6 m × 3 m is 10.8 m², about 116 sq ft (10.8 × 10.764). A round patio 3 m across is π × 1.5² ≈ 7.07 m².

Sur le chantier

The living room with a dining nook. An L: the main room tapes 18 ft × 14 ft and the nook off the corner 10 ft × 8 ft. Two rectangles, 252 + 80 = 332 sq ft. Run the tool twice, or put the main room in and add the nook by hand — either way, never try to find "the" length and "the" width of an L. There is not one. In metric the same L is 5.5 × 4.3 m plus 3 × 2.4 m: 23.65 + 7.2 = 30.85 m².

A gable end for siding. The wall is 24 ft wide and 8 ft to the plate, and the gable peaks 6 ft above that. The rectangle is 24 × 8 = 192 sq ft; the triangle on top is half the base times the height, 24 × 6 ÷ 2 = 72 sq ft. Total 264 sq ft of siding before the window comes off. A triangle is always half of the rectangle that would enclose it — that is the whole trick. (Metric: 7.3 m wide, 2.4 m to the plate, a 1.8 m gable — 17.52 + 6.57 = 24.09 m².)

Roof area from the footprint. A 30 ft × 40 ft footprint is 1,200 sq ft of attic floor, not of roof. The roof surface is longer because it slopes: multiply the footprint by the rafter multiplier for the pitch (the roof pitch tool gives it — 1.118 for a 6/12), so 1,200 × 1.118 = 1,342 sq ft of shingles, and that is before the overhangs. A 9 m × 12 m footprint is 108 m², and at a 6/12 pitch 108 × 1.118 = 120.7 m² of roof.

Exercez-vous

Quick referencefor area

Square feet in a square metre: 10.76 — or ft² × 0.0929 = m²
Square inches in a square foot: 144
Square feet in a square yard: 9
Inches as feet: 6 in = 0,5 · 8 in = 0,667 · 9 in = 0,75 · 30 in = 2,5 · 32 in = 2,667
Triangle: base × height ÷ 2
Millimetres as metres: 600 mm = 0,6 · 900 mm = 0,9 · 1 200 mm = 1,2 · 2 400 mm = 2,4
Circle from the diameter: 0.785 × d² (a 10 ft circle is 78.5 sq ft · a 3 m circle is 7.07 m²)
An acre: 43,560 sq ft — about 209 ft square
A hectare: 10,000 m² — 100 m square · about 2.47 acres

Waste & overagewhat to add, and why

Area is what the other tools multiply, so the overage belongs on those pages — but if you are ordering a product straight from an area (sod, membrane), most crews add 5–10% for the cuts along the edges and the piece that gets damaged.

Mistakes to catchbefore you order

Measuring an L-shaped room as one rectangle across its widest points; split it into two and add the parts.
Reading a 32 in width as 3.2 ft — it is 2.67 ft; convert inches to decimal feet before you type, or use feet-inches.
Forgetting the closet, the bay window or the alcove that the floor goes into.

La formule

rectangle: area = length × width · circle: area = π × (diameter ÷ 2)²

Area is a length times a length, so its unit is a square: feet × feet gives square feet. Converting to metric squares the length factor too, which is why the number is 0.0929 per square foot rather than 0.3048.

Questions

How do I calculate square footage?: Multiply length by width for a rectangle. A 12 ft by 10 ft room is 120 square feet; in metric, a 3.6 m by 3 m room is 10.8 m². For a circle, it is π times the radius squared — or use the diameter option here and let the tool do it. For an L-shaped room, split it into rectangles, work out each, and add them together.
How do I convert square feet to square metres?: Multiply square feet by 0.0929, or divide by 10.764. This tool shows both at once, so a 120 sq ft room reads as about 11.15 m² without you touching a conversion. The factor is just the square of the foot-to-metre ratio (0.3048² = 0.0929).
Do I subtract doors and windows?: It depends what the area is for. For flooring, work with the full floor area. For wall paint or drywall, subtract large openings if you want a tighter number, though many people leave them in as built-in waste. This tool gives you the gross area; subtract openings yourself where it matters.
How much extra should I add for waste?: Square footage itself is just the measurement, so this tool does not add waste — it gives the true area. Add the waste on the material tool instead: flooring, tile and drywall calculators apply a waste factor to the area you bring them.

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