Skip to content
ToolBoxGeniehome

Square Footage Calculator

Calculators · Added

Measure the room, get the area. This takes lengths in feet, inches, yards, metres or centimetres, applies the right formula for the shape you actually have — including circles, triangles and L-shaped rooms — and adds up as many separate areas as the job needs. A waste allowance and a price per unit turn the answer into something you can take to a supplier.

Room 1

length × width

ft
ft
%

Cuts, offcuts and breakages. 10% is typical for straight flooring.

sq ft

Optional — from the box.

Optional.

How to use the square footage calculator

  1. 1Pick the shape that matches the area you measured, and the unit your tape measure was in.
  2. 2Enter the dimensions the shape asks for. An L-shaped room is entered as two rectangles.
  3. 3Use Add another area for each additional room, and each keeps its own shape and unit.
  4. 4Choose the unit you want the answer in, and set a waste allowance — 10% covers ordinary cutting.
  5. 5Optionally add the coverage printed on the box and a price, to get packs to buy and a total cost.

Examples

A rectangular bedroom

Input
12 ft × 14 ft
Result
168 sq ft — 185 sq ft with 10% waste

The waste allowance is what stops a job ending one plank short. Diagonal or herringbone laying needs closer to 15%.

Mixed units across two rooms

Input
Room 1: 4.2 m × 3.6 m · Room 2: 10 ft × 8 ft
Result
162.8 sq ft + 80 sq ft = 242.8 sq ft

Each area carries its own unit, so a metric plan and an imperial measurement can be added without converting anything by hand first.

A circular patio

Input
Diameter 12 ft
Result
113.1 sq ft

Diameter, not radius — halving it is the step people skip, and it makes the answer four times too large.

About the square footage calculator

Measuring a room properly

Rooms are rarely as square as they look. Measure each wall at both ends rather than once in the middle, and if the two readings differ, use the larger. A wall that is out by three centimetres over four metres is completely normal in a built house, and it is the difference between a tile run that finishes flush and one that leaves a tapering sliver down the last row.

Measure to the wall, not to the skirting, if the skirting is coming off. Measure into door recesses if the flooring will continue through them, because a doorway adds a surprising amount over several rooms. And write the numbers down as you take them rather than trusting them to memory — the most common error in a floor order is not arithmetic, it is a transposed pair of digits.

For an irregular plot, the reliable method is to draw the outline roughly to scale on paper, divide it into rectangles and triangles with straight lines, and measure each piece separately. The shapes here are chosen to cover what that decomposition produces. A curve can be approximated as a series of triangles, which is close enough for ordering turf and not close enough for anything structural.

Where the square-foot figure goes next

Materials are sold by coverage, and the coverage is printed on the box in whichever unit the manufacturer prefers. Setting the output unit here to match the box before dividing removes a conversion step, and with it the most common source of a wrong order. Twenty boxes covering 1.5 m² each is 32.3 sq ft of coverage, and comparing that to an area in square feet without converting is how a job ends up 30% short.

Rent and property listings use area differently again. A flat advertised at 1,200 sq ft is usually quoting built-up area, which includes internal walls, and sometimes super built-up, which adds a share of the corridors and lobby. The carpet area — what you can actually put furniture on — can be twenty to thirty per cent less. Measuring the rooms yourself and adding them gives the carpet area, which is why the two numbers so often disagree.

For land, the useful conversions are that an acre is 43,560 sq ft and a hectare is 10,000 m². Neither is a tidy number in the other system, which is why plot sizes are so often quoted in whichever unit makes them sound larger.

Frequently asked questions

How do I measure an L-shaped room?
Split it into two rectangles and add them. Choose the L-shape option and enter the main rectangle first, then the leg — the trick is to make sure the two do not overlap, so measure the leg from where the main rectangle ends rather than from the wall. Any awkward floor plan can be handled the same way: break it into shapes this tool knows, add an area for each, and let them total.
Why is my square metre figure so much smaller than the square feet?
Because a square metre is about 10.76 square feet, so the number in metres is roughly a tenth of the number in feet for the same floor. If your two figures differ by about three rather than about eleven, a length conversion factor has been used where an area one was needed — the factor between feet and metres is 0.3048, but between square feet and square metres it is 0.3048 squared, which is 0.09290304.
How much waste should I allow?
Ten per cent is the usual starting point for straight-laid flooring or tiles in a simple rectangular room. Go to fifteen for diagonal or herringbone patterns, for rooms with alcoves and door recesses, and for anything with a repeating pattern that has to line up, because matching the pattern throws away more offcuts. Large-format tiles waste more than small ones. Ordering the extra is cheaper than a second delivery, and the spares are what you use when one gets damaged later.
Should I subtract the area under kitchen units or a fitted wardrobe?
Generally no. Flooring is usually laid under and around fitted furniture, and even where it is not, having the material continue underneath means a future change of layout does not leave a bare patch. The one case for subtracting is a permanent built-in island or a fixed hearth that will certainly never move. When in doubt, include it — the difference is a fraction of a box.

Related tools