Square Footage Calculator
Measure every room, add them up once, and get the total in square feet and square metres — with an allowance for offcuts and a price per square foot on the end of it. Rectangles, L-shapes, circles and triangles, as many rooms as the job has.
The rooms you measured
Five to ten percent covers offcuts and part-planks at doorways. Go to fifteen or twenty for a diagonal or herringbone layout, or for a wide-plank floor with a repeating grain to match.
Leave it blank for a plain measure-up. Quotes for flooring, tile, carpet, and turf are all written per square foot, so this is the number on the estimate.
Printed on the carton — 25.6 and 23.31 square feet are common for plank flooring. Cartons are counted in whole boxes, because that is how they are sold.
2 rooms measured, or 37.16 m². With a 10% allowance for offcuts you would buy 440 sq ft.
- Net floor area
- 400 sq ft
- In square metres
- 37.16 m²
- Waste allowance (10%)
- 40 sq ft
- Order this much
- 440 sq ft
| Room | Square feet | Square metres | Share of total |
|---|---|---|---|
| Living room | 280 sq ft | 26.01 m² | 70% |
| Kitchen | 120 sq ft | 11.15 m² | 30% |
- Measure to the inside face of the wall. A real-estate listing measures to the outside, which is why the same house is several percent bigger on the listing than on the flooring quote.
- The waste allowance is shown on its own line so you can argue with it. It is a guess about your rooms and your layout, not a constant.
- Cartons are rounded up to whole boxes. Buy the surplus in the same order — a later carton is a different production run and will not match.
Four shapes, one project total
Every row reduces to an area in square feet, and the project is the sum of the rows. Nothing is rounded until the end: each room is rounded to the hundredth for the table, but the total accumulates the raw values, so adding the printed column by hand can differ from the printed total in the second decimal place and the total is the one that is right.
Arect = L × W • AL= L × W − c × d • Acircle= π × (D ÷ 2)² • Atri = ½ × b × h- L, W
- Length and width of the room in feet, measured at floor level
- c, d
- The two sides of the corner missing from an L-shaped room
- D
- Diameter of a round room, across its widest part, in feet
- b, h
- Base of a triangular space and the square distance from that base to the far corner
- × 0.09290304
- Square feet to square metres, exact by definition: the foot is 0.3048 metres
The waste allowance is applied to the project total rather than room by room, because material moves between rooms. A board cut short at the end of a run in the hallway starts the next run in the bedroom. Allowing for offcuts once, on the whole order, is both cheaper and closer to how the floor actually goes down.
Cartons are then the order divided by the coverage printed on the box, rounded up. Never to the nearest carton: 17.19 boxes is 18 boxes, because the store does not sell the other four fifths.
A living room and a kitchen, quoted for engineered oak
The living room is 20 by 14 feet, so 20 × 14 = 280 square feet. The kitchen is 12 by 10, so 120. Together the project is 400 square feet, or 400 × 0.09290304 = 37.16 square metres.
A 10% allowance for offcuts adds 40 square feet, so the order is 440 square feet. At $4.50 a square foot the material is $1,980, of which $180 is the allowance — a line worth seeing, because it is the one you can argue with. Drop to 5% and the same job is $1,890; go to 20% for a herringbone layout and it is $2,160. The floor did not change size.
Engineered oak often comes in 25.6 square foot cartons. 440 ÷ 25.6 = 17.19, so you buy 18 cartons, which is 460.8 square feet and leaves 20.8 spare. That surplus is not waste. It is the plank you will want in three years when a radiator leaks, and a carton bought later comes from a different production run — a different batch of veneer, a different lot of stain — and will not match the floor it is patching.
Now the part the quote will not mention. If this is a whole apartment listed at 400 square feet, it is not: the listing measured the walls too. Read on.
The same room has two honest square footages
Where you put the tape changes the answer by several percent, and the two conventions that matter disagree deliberately.
ANSI Z765 — the standard most United States residential listings and appraisals follow — measures gross living area to the exterior finished surface of the exterior walls and does not deduct interior partitions at all. A 30 by 50 foot footprint is 1,500 square feet of gross living area, walls included, regardless of how it is divided inside.
A flooring or tiling quote measures the floor you can see. Take six inches off each exterior wall and that same footprint is 29 by 49 = 1,421 square feet before a single interior wall, a stair opening, or a run of kitchen units is subtracted. That is 5.3% gone to the exterior walls alone; count interior partitions at four and a half inches apiece and eight to twelve percent is the ordinary gap on a normal house.
Neither figure is wrong and neither is a trick. An appraiser is valuing a building, so the building is what gets measured; a flooring contractor is selling material for a surface, so the surface is what gets measured. The failure mode is using one number for the other job — ordering flooring against a listing square footage buys roughly a tenth more material than the floor needs, and quoting a listing from an interior measure-up undersells the house.
This calculator measures the floor. Enter room dimensions taken at floor level, inside face to inside face, and the total is what you can walk on.
Which area tool you actually want
Use this page if you are adding rooms up to buy something; use the area calculator if you have one shape and want the area it encloses; use the area converter if you already have an area and need it in different units.
- Area of a shape calculator — for geometry rather than a project. Ten plane figures, including a trapezoid, a sector, an ellipse, and a triangle from three side lengths by Heron’s formula, with the perimeter where the dimensions pin one down. It returns a bare number in whatever unit you measured in.
- Area converter — for units rather than geometry. Square feet to square metres, acres to hectares, square miles to square kilometres. Use it once you have an area and need it expressed differently.
The three overlap in a search box and nowhere else. Keeping them apart is what lets this one carry an editable room list, a waste allowance and a price per square foot instead of a units table crammed in beside a shape picker.
The offcut at the end of every run has to come from somewhere
Flooring arrives in fixed lengths and a room is rarely a whole number of them. Every run ends in a cut, and the piece left over only gets reused if it is long enough to start the next run — the usual rule is six or eight inches minimum, below which it goes in the skip. Doorways cost a part-plank each. A pattern that repeats costs you whatever has to be discarded to keep it lined up.
Five to ten percent covers that for a straight layout in an ordinary rectangular room. A diagonal or herringbone installation is a different problem: every board meets the wall at an angle, so every cut produces a wedge that fits nowhere, and fifteen to twenty percent is normal. Wide planks waste more than narrow ones. Rooms full of alcoves waste more than open ones.
The allowance is kept on its own line here, in square feet and in money, for the same reason the waste line exists on the concrete calculator: an allowance folded into a total is invisible, and an invisible allowance is one nobody ever checks. Change it, watch the cost move, and decide for yourself.
What this calculator assumes
- Dimensions are the floor you can walk on — measured at floor level, inside face to inside face. That is the flooring convention, not the ANSI Z765 listing convention, and the two differ by several percent.
- Nothing is deducted for kitchen units, fitted wardrobes, stair openings, hearths, or islands. Measure round them and enter the remainder if they are large enough to matter.
- The waste allowance is a guess about your rooms and your layout, not a constant. It is applied to the project total rather than room by room, because offcuts move between rooms.
- Cartons are rounded up to whole boxes and the count is taken from the order figure, after waste. Buying the surplus in the same order matters: a later carton is a different production run and will not match.
- An L-shaped room is a rectangle with one rectangular corner removed. A room with two notches is two rows, or one row plus a negative you work out yourself.
- Square metres are exact conversions, not separate measurements: the foot is defined as 0.3048 metres, so a square foot is 0.09290304 square metres by definition.
Square footage calculator FAQ
How do I calculate the square footage of a room?
Multiply the length by the width, both in feet. A room 20 feet by 14 feet is 280 square feet. If the room is not a rectangle, split it: an L-shaped kitchen is a rectangle with a smaller rectangle taken out of one corner, a bay is a rectangle plus a triangle at each end, and a round turret is π × (diameter ÷ 2)². Measure at floor level rather than at waist height, because skirting, radiators and kitchen units all lie about where the wall is.
Is square footage measured to the inside or the outside of the walls?
It depends who is asking, and the gap is not small. ANSI Z765, the standard most United States residential listings follow, measures gross living area to the exterior finished surface of the exterior walls and does not deduct interior partitions at all. A flooring contractor measures the floor you can actually see — inside face to inside face, minus whatever the cabinets stand on. On a 30 by 50 foot footprint with six-inch exterior walls, the listing figure is 1,500 square feet and the floor inside it is 1,421, about five percent less before a single interior wall is counted. Both numbers are correct. They answer different questions.
How much extra flooring should I order?
Five to ten percent over the measured area for a straight layout in an ordinary room, and that is what the default allowance here does. Push it to fifteen or twenty percent for a diagonal or herringbone installation, where every board meets the wall at an angle and the offcut is rarely reusable; for a wide plank with a strong repeating grain that has to be matched across a run; or for a floor plan full of alcoves, closets and doorways, because each one costs you a part-plank. Rooms that are close to a whole number of board widths waste less than rooms that are not, which is why the allowance is a guess rather than a constant.
How many square feet are in a square metre?
10.7639. The foot is defined as exactly 0.3048 metres, so a square foot is exactly 0.09290304 square metres and a square metre is 1 ÷ 0.09290304 = 10.76391 square feet. Both conversions here are exact by definition rather than measured, which is why the square-metre column can be trusted to the same precision as the square-foot one.
Does square footage include the garage, the basement, or the closets?
Under ANSI Z765, closets and hallways are included because they sit inside the finished, heated envelope; an attached garage is excluded because it is not finished living space; and a below-grade basement is reported separately from above-grade living area even when it is finished to the same standard. That last rule is why a listing will say something like 1,800 square feet with a further 900 finished below grade rather than 2,700. For a flooring order none of this matters — you are buying material for every floor you intend to cover, garage included if you are covering it.
How do I measure a room that is not a rectangle?
Break it into shapes you can measure and add them as separate rows. An L-shaped room is handled directly here: give the overall length and width, then the length and width of the missing corner. Anything stranger — a bay window, a splayed wall, a curved bar — splits into a rectangle plus a triangle or a part-circle. Add the rows rather than the answers: the total is what carries the waste allowance and the price, and adding separately-rounded subtotals is how a measure-up drifts.
Why is my house smaller on the flooring quote than on the listing?
Because the listing measured the building and the quote measured the floor. Exterior walls are typically five to seven inches thick once sheathing and finish are counted, interior partitions another four and a half, and none of that is floor. Add the footprint of kitchen units, a fitted wardrobe, a stair opening and a hearth, and the difference between a listed square footage and a floorable one is routinely eight to twelve percent on a normal house. Neither party is being dishonest; measure the rooms yourself and you will get the flooring number.
Sources and review notes
- ANSI Z765, Square Footage — Method for Calculating: Single-Family Residential, administered by Home Innovation Research Labs — the standard behind the listing convention described above, including measuring to the exterior finished surface and reporting below-grade area separately
- NIST Special Publication 811, Guide for the Use of the International System of Units — the definition behind the square-metre column: the foot is exactly 0.3048 metres, so the square foot is exactly 0.09290304 square metres
The geometry and the unit conversion here are exact and have nothing behind them to go stale. The two figures that move are the waste allowance, which is a rule of thumb rather than a published constant, and the carton coverage, which is printed on the box and differs by product. Check both against the material you are actually buying.