Square feet and room area calculator
Square footage is length times width in feet: a 12 × 10 ft room is 120 ft², or 11.15 m². The same panel handles a circle as πr² and a triangle as half base times height, and for a whole room it returns floor area, net wall area, ceiling area, perimeter and volume from one measurement.
How to calculate square feet
The mistake that ruins a square-footage figure is mixing units mid-measurement: taking a room as 12 feet 6 inches and entering 12.6 rather than 12.5. Six inches is half a foot, not six tenths, and the error compounds across both dimensions. Where a room is genuinely irregular, splitting it into rectangles and adding them is more accurate than trying to average, and it is also how a flooring supplier will quote it. Alcoves, bay windows and chimney breasts each want their own small rectangle.
One measurement answers four questions, which is why the room mode exists. Floor area orders the flooring. The perimeter is the length of skirting, coving or beading you buy, and the run for a wallpaper order. Wall area is the perimeter times the height. And the volume figure, the one people skip and then need, sizes heating, cooling and ventilation, because air conditioners and dehumidifiers are rated against the volume of air they have to move.
Which wall figure you use depends on the material, and this is where materials lists go wrong. Paint and wallpaper follow the net area, because you genuinely do not cover a window. Plasterboard and insulation follow the gross area, because sheets are cut around openings and the offcut is usually scrap. Skirting and coving follow the perimeter minus the door widths. Using one number for all three is how an order ends up simultaneously over on paint and short on board.
Ceilings look like the simplest case and have one trap. A flat ceiling is exactly the floor area, but a sloping one is not: for a single slope, multiply by the rafter multiplier for that pitch, which adds about 15% at 30 degrees. A room-in-roof with two slopes and a flat section wants each plane measured separately. Ceilings also drink more paint than a wall of the same size, because rolling upward puts the coat on thinner.
What people use it for
- Measuring a room before ordering flooring or carpet
- Converting a listing in square feet to square metres
- Sizing a patio, lawn or garden bed
- Working out rent or price per square foot
- Getting floor, wall, perimeter and volume from one measurement
- Working out paintable area after doors and windows
- Measuring a ceiling for paint, board or coving
- Ordering plasterboard or insulation by the sheet
- Sizing a radiator or an air conditioner from room volume
- Ordering skirting or coving by the perimeter
- Comparing two rooms in a property listing on the same basis
- Sizing an acoustic or insulation treatment for a ceiling
- Checking a decorator’s measured quote against your own tape
Questions
Multiply length by width, both measured in feet. For 12 ft 6 in, use 12.5 rather than 12.6.
10.764. Going the other way, one square foot is 0.0929 square metres.
Split it into two rectangles, calculate each, and add them. That is also how a supplier will quote it.
For flooring, yes if the floor continues into them. For carpet, ask the fitter: some measure the largest rectangle instead.
Add the four wall widths for the perimeter, multiply by the height, then deduct doors and windows.
The panel takes 1.8 m² off for each door, a 0.9 × 2.0 m opening, and 1.44 m² for each window, a 1.2 × 1.2 m one. Narrower doors are common: a 0.76 × 2.0 m UK internal door is 1.5 m², and a US door at 32 × 80 inches about 1.65 m², so on a wall of those the deduction runs a little generous and the paint or paper is worth rounding up.
No. Board is cut around openings and the offcut rarely gets reused, so order on the gross area.
Treat the sloping wall as a trapezoid: average the tallest and shortest heights, then multiply by the width.
For a flat ceiling, yes, and it is worked out separately from the walls because it usually gets its own coat count. For a sloping one, multiply by the pitch multiplier: a 30 degree slope adds about 15%.
Divide the area by the sheet area, 2.88 m² for a standard 2.4 × 1.2 m sheet, then add one for cuts.
It follows the room perimeter. Add about 10% for mitred corners, which each waste a short offcut.
It sizes heating, cooling and ventilation. Air conditioners and dehumidifiers are rated by the volume of air they can handle.
At floor level for area, since that is what flooring covers. Walls can bow, so measure the widest point if the two differ.
Not always. Property listings sometimes exclude areas under a low sloping ceiling, so check the definition being used.