Most rooms are not rectangles, and most calculators only take one. This one adds up as many sections as you need and gives you the answer in square feet, square metres and square yards at the same time.
Enter each rectangular section of the space. L-shaped room? That is two rectangles. Bay window? Three. Add them up and get the total.
Works in metric and US imperial — you choose at the start and can switch at any time. Every figure this calculator uses is published with its source, and the result comes with a printable order sheet. No account, no email, and nothing you type leaves your browser.
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Every section is a rectangle: length × width. The calculator adds as many sections as you give it and returns the total in square feet, square metres and square yards at the same time, because materials are quoted in all three and converting on a phone in a shop aisle is where mistakes happen.
A 12 × 10 ft room is 120 sq ft — which is 11.15 m², or 13.3 sq yd. If the same room has a 3 × 2 ft chimney breast, measure the two alcoves either side as their own small rectangles and add them, rather than subtracting the breast from the whole: same answer, fewer ways to slip.
Measure at the widest point, and measure twice. Walls are rarely parallel — if a room is 3.4 m at one end and 3.5 m at the other, use 3.5, because every material calculator on this site rounds up and the extra costs far less than a second delivery. Keep the section list written down: it is what a supplier will ask for if the quantity is ever queried, and it saves measuring the room again next time.
Split it into rectangles and add them up — an L-shape is two rectangles, a bay window is three. It is exact, not approximate, and it is what the trade does. Measure alcoves as separate sections rather than subtracting, which is easier to get right.
Nine, not three. A yard is three feet, so a square yard is 3 × 3 = 9 square feet. It catches people constantly — carpet quoted per square yard is about nine times the per-square-foot price, which looks alarming until you do the arithmetic.
Circles: multiply the radius by itself, then by 3.14. A 3 m diameter circle has a 1.5 m radius, so 1.5 × 1.5 × 3.14 = 7.07 m². Triangles: base × height ÷ 2.
No. Painting needs wall area — perimeter × height, minus doors and windows — which is usually two to three times the floor area. Roofs are the same trap in the other direction: a pitched roof has more surface than the footprint under it.