Home & construction
Square footage calculator
Measure the shape you actually have, not the rectangle you wish you had. L-shaped rooms, circles and triangles are all handled, with cost and coverage from the total.
Offcuts and breakage. 10% is standard, 15% for diagonal or patterned layouts.
Break the room into rectangles
Almost every real room can be handled by splitting it into rectangles and adding or subtracting them. An L-shaped room is one big rectangle minus a corner. A room with a bay window is a rectangle plus a trapezoid. Alcoves add, chimney breasts and kitchen islands subtract.
Work in one unit throughout. Mixing feet and inches inside a single calculation causes more errors on site than any other habit — 12 feet 6 inches is 12.5 feet, not 12.6.
Why measurement error scales
Area multiplies two measurements, so a small error in each compounds. Being 2% out on both length and width leaves you about 4% out on area. On a 200 square foot floor at $6 a square foot, that is a $50 mistake before waste.
Measure the longest and widest points, take the measurement twice from different corners, and check whether the room is actually square. Older buildings routinely have walls out by an inch or more across a room, which is exactly the sort of thing that turns a tidy tile layout into a visible taper along one wall.
Waste allowances that actually reflect the job
| Job | Typical allowance | Why |
|---|---|---|
| Straight-lay flooring, simple room | 7–10% | Offcuts at the end of each row |
| Diagonal or herringbone | 15–20% | Every edge cut wastes a piece |
| Patterned or large-format tile | 15% | Pattern matching and breakage |
| Irregular room, many corners | 15% | More cuts, more offcuts |
| Carpet from a roll | varies | Depends on roll width against room width |
Buying a little extra of the same batch is nearly always cheaper than a second delivery later, and dye lots or tile batches rarely match across orders. Keeping a few spare pieces for future repairs is also worth the shelf space.
Square feet, square metres and the confusing ones
A square yard is nine square feet, not three — squaring the linear conversion squares the factor too. The same trap catches square metres: one square metre is 10.764 square feet, not 3.28. Getting this backwards is a common and expensive error when ordering from suppliers who quote in a different system.
One more warning: flooring, carpet and turf are often sold by the linear metre or linear foot off a fixed-width roll, which is a length, not an area. Check which you are buying before comparing prices.
Common questions
How do I calculate square footage of a room?
Multiply length by width in feet. For a 12 by 10 foot room that is 120 square feet. Convert inches to a decimal first by dividing by 12, so 12 feet 6 inches becomes 12.5. For rooms that are not rectangular, split them into rectangles and add the parts.
How many square feet in a square metre?
About 10.764. The conversion squares the linear factor: since a metre is 3.281 feet, a square metre is 3.281² square feet. Going the other way, divide square feet by 10.764 to get square metres.
How much extra flooring should I buy?
Ten percent for a simple rectangular room with straight-lay planks, and fifteen to twenty for diagonal, herringbone or heavily patterned layouts, or for rooms with many corners and doorways. Buy it all in one order so the batch matches, and keep the offcuts for repairs.
Do I include closets and alcoves in floor area?
For material ordering, include anything you are covering — which usually means closets, since flooring normally runs into them. For property listings the rules differ by market and by measurement standard, and enclosed unheated space is often excluded. If the number is going on a listing, check which standard applies locally.