Reference
Flooring square footage and waste
Every flooring order starts with one number, and the number is almost never the one printed on the floor plan. Rooms are out of square, the floor runs into places the plan does not show, and between the measurement and the delivery sits a waste allowance that people guess at. Here is how to arrive at the figure, and what to add to it.
How to figure square footage for flooring
Break the space into rectangles, measure each one in feet, multiply length by width, and add the results. That is the whole method — the difficulty is never the arithmetic, it is deciding where one rectangle ends and the next begins, and remembering the parts of the floor nobody draws.
Measure each rectangle at its widest point, and measure it at both ends. Walls are rarely parallel: a twenty-foot room that is two inches wider at one end is completely normal, and the floor has to fit the wide end. Take the larger figure both times.
| What you are measuring | How to handle it | Watch for |
|---|---|---|
| Plain rectangle | Length × width | Measure both ends — take the wider one |
| L-shaped room | Split at the inside corner into two rectangles | The overlap belongs to one rectangle, not both |
| Bay or bump-out | Its own rectangle, added on | Usually 4–8 sq ft, and the floor always runs into it |
| Closet | Its own rectangle, added on | Left off most plans; the floor still goes in |
| Doorway | Add the depth of the jamb across its width | About 0.5–1 sq ft each, and easy to forget × 6 |
| Stair opening | Subtract it | The one hole in a normal floor worth subtracting |
| Angled or curved wall | Rectangle to the widest point | The offcut is real waste — count it in the allowance |
What to subtract, and what to leave in
There is a single test, and it settles almost every case: if the thing can be pulled out of the room without a saw, the floor goes underneath it and it does not come off your figure.
That puts appliances firmly in. A dishwasher is removed for service and a refrigerator is rolled out to clean behind, and a floor that stops at their front edge traps both of them in place — it is one of the most common and most expensive flooring mistakes there is. Furniture, rugs and freestanding cabinets are in for the same reason.
| Subtract it | Leave it in |
|---|---|
| A kitchen island fixed to the subfloor | Dishwashers, refrigerators, ranges |
| A hearth or a fireplace base | Freestanding furniture and rugs |
| The stair opening | Toe-kicks the floor slides under |
| Base cabinets built in place | Radiators and their feet |
| A built-in tub or shower base | Anything under about 10 sq ft |
The last row is the one to trust. Subtracting a four-square-foot obstruction from a three-hundred-square-foot room changes the order by nothing at all — the waste allowance is larger than the saving, and the planks cut around it cannot be used anywhere else anyway. Small holes cost material rather than save it.
How much extra flooring to buy
The allowance is not padding and it is not a safety margin. It is the offcut pile: the end of every row that is too short to start the next one, the plank ripped down the last row, the board with a defect you cull, and the one you cut the wrong way round. Layout drives it far harder than room size does.
| Material and layout | Add | Where it goes |
|---|---|---|
| Laminate or vinyl plank, straight, simple room | 5% | Each row ends in an offcut that leads the next |
| Laminate or vinyl plank, straight, many corners | 10% | Every alcove and closet restarts the row |
| Plank at 45°, diagonal | 15% | Every perimeter plank is cut at an angle |
| Herringbone or chevron | 15–20% | Angled cuts on all four walls, both directions |
| Solid hardwood, nailed and racked | 5–10% | Offcuts plus the boards you cull for grade |
| Engineered plank | 5–8% | Same cuts, fewer culls — the grade is selected |
| Carpet pad and foam underlayment | 5% | Seams butt together, so almost nothing is lost |
| Carpet or sheet vinyl | not a percentage | Roll width decides it — see below |
Keep a full box back when the job is done. Flooring is made in batches and the shade drifts between them, so a box bought in a year to repair a water-damaged corner will rarely match the floor around it. The spare box is cheaper than the mismatch.
Why carpet is not measured in square feet
Carpet comes off a roll, and the roll is a fixed width — 12 ft as standard in the US, with 13 ft 2 in, 13 ft 6 in and 15 ft also made. You buy length off that width, so the room is not compared against an area at all. It is compared against the roll.
A room 14 ft wide does not need 17% more carpet than a room 12 ft wide. It needs a second width, because the first one falls two feet short — and the strip left over after the seam is offcut you have paid for and will never walk on. The same 14 ft room off a 15 ft roll wastes a single foot instead. Two rooms of identical area can differ by a third in what they cost to carpet, purely on how they sit against the roll.
Which is why the seam matters as much as the total. Run seams in the direction of the main light rather than across it, never across a doorway, and keep them out of the busiest path through the room. The carpet calculator lays the room out against each roll width and shows the offcut for both, which is the only honest way to compare two prices per square foot.
How many boxes of flooring you need
Coverage per box is printed on the carton and varies more than people expect, because a box holds a fixed number of planks rather than a fixed area. A thicker, wider plank means fewer square feet in the same box at a higher weight. Always divide by the figure on the box you are actually buying, and always round up.
| Covering | Sold as | Typical coverage | Worth knowing |
|---|---|---|---|
| Laminate | Box | 20–24 sq ft | Wider and thicker boards cover less per box |
| Vinyl plank (LVP) | Box | 24–30 sq ft | Rigid core boxes run 40–55 lb — plan the carry |
| Engineered wood | Box | 20–30 sq ft | Long-board boxes are awkward rather than heavy |
| Solid hardwood | Bundle | 20–24 sq ft | Sold by the bundle, priced by the square foot |
| Carpet | Cut from a roll | 12 sq ft per linear ft on a 12 ft roll | Length off a fixed width, never area |
| Carpet pad | Roll | ~270 sq ft (6 × 45 ft) | Seams taped; order against room area plus 5% |
| Foam underlayment | Roll | 100–200 sq ft | Check whether the plank already carries a pad |
The last two rows are a separate order from the floor above them. The underlayment calculator sizes the rolls for either, and carpet pad thickness and density covers which specification a room actually needs before you count rolls of it.
The formula, start to finish
net area = area − permanent obstructions
order area = net area × waste factor
boxes = ⌈ order area ÷ coverage per box ⌉
Measuring in metres instead? Multiply square metres by 10.764 to get square feet, or divide square feet by 10.764 to go back. A room 4.2 × 3.6 m is 15.12 m², which is 162.7 sq ft — and every figure on this page then applies unchanged.
The flooring calculator runs this for a whole floor at once and converts the result into the units each covering is sold in. For a cut plan that shows where the joints land rather than an area, the per-material calculators — laminate, vinyl plank and hardwood — lay the boards out row by row and count the offcuts they actually produce.
Work out your floor area →