Area for a rectangle, circle or triangle, converted to square feet, square metres, square yards, acres and hectares at once.
Rectangle: length × width. Circle: π × radius², where the radius is half the diameter — measuring the diameter and halving it is far more reliable than trying to find the exact centre. Triangle: half × base × perpendicular height, where the height is measured at a right angle to the base, not along a sloping side.
For any room that is not one of these, break it into pieces that are, work out each, and add them. An L-shaped room is two rectangles. A room with a bay window is a rectangle plus a partial circle. This is how flooring estimators actually work — nobody has a formula for an L.
| From | To | Multiply by |
|---|---|---|
| Square feet | Square metres | 0.0929 |
| Square metres | Square feet | 10.764 |
| Square feet | Square yards | ÷ 9 |
| Square feet | Acres | ÷ 43,560 |
| Acres | Hectares | 0.4047 |
| Square metres | Hectares | ÷ 10,000 |
The one that catches people is square yards: a yard is three feet, so a square yard is nine square feet, not three. Carpet is often priced per square yard while rooms are measured in feet, and forgetting to divide by nine rather than three produces a quote three times too high.
This is not sloppiness — different trades measure to different conventions on purpose.
Gross floor area measures to the outside of exterior walls and includes wall thickness. Net or usable area measures the inside faces, which is what you can actually put furniture on. Carpet area, the term used in Indian real estate and now legally defined under RERA, excludes wall thickness entirely and is smaller again. A flat advertised at 1,200 sq ft "super built-up" — which loads a share of lobbies, stairs and amenities onto the number — might have a carpet area closer to 800.
When comparing properties or briefing a contractor, establish which convention is in use before comparing numbers. They can differ by 25% or more for the identical space.
Rooms are rarely truly square. Measure length and width in at least two places each and use the larger figure if you are ordering material, the smaller if you are checking whether something fits. For flooring, measure at floor level rather than at waist height, since walls are not always plumb.
For land, pacing gives a usable rough figure — an average adult stride is close to 2.5 feet — but anything involving a boundary or a transaction wants a proper survey. Property lines are legal instruments and a fence is not evidence of one.
Divide it into rectangles, triangles and circle segments, work out each one, and add them together. An L-shaped room is two rectangles; a room with an alcove is a rectangle plus a smaller rectangle. Sketch it, mark the dimensions on the sketch, and check the sub-dimensions add up to the overall ones — that catches most measurement errors before they become ordering errors.
About 10.764. Going the other way, one square foot is 0.0929 square metres. The relationship is not the linear conversion squared by accident — it is exactly that: 3.28084 feet per metre, squared, gives 10.764. This is the same reason a room twice as long and twice as wide has four times the area, not twice.
Because different conventions measure different things. Gross floor area includes wall thickness and is measured to the outside of the building. Usable or net area is the inside faces. In India, "super built-up area" adds a proportional share of lobbies, stairways and shared amenities, and can be 25 to 40% larger than the carpet area you can actually walk on. RERA now requires carpet area to be disclosed for exactly this reason.
43,560 — an oddly specific number that comes from the medieval definition of an acre as one chain by one furlong, or 66 feet by 660 feet. A hectare, being a clean 10,000 square metres, is about 2.47 acres. For rough mental work, an acre is a little smaller than an American football field including the end zones.
Yes, and the amount depends on the pattern. Ten percent covers a straightforward straight lay in a simple rectangular room. Fifteen percent is more realistic for a diagonal layout, a herringbone pattern, a room with many angles, or planks with a directional grain that has to be matched. Buying slightly over from the same production batch is also worth doing — dye lots vary, and a later top-up may not match.
Related: Tile Calculator · Concrete Calculator · Area Calculator · Roofing Calculator Once you have the area: the BTU Calculator sizes heating and cooling for it, the Mulch Calculator and Gravel Calculator convert it to cubic yards at a chosen depth. Decorating rather than building? The Paint Calculator turns wall area into litres or gallons, with doors and windows deducted.