Flooring Calculator
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Result
Boxes to buy
- Floor area
- 400 sq ft
- Area including waste
- 432 sq ft with 8% waste
- What those boxes cover
- 446.6 sq ft
- Keep as attic stock
- 1 unopened box (20.3 sq ft)
- Underlay
- 400 sq ft, if the product has none attached
- Perimeter for trim
- 82 ft of skirting or quarter-round
- Leave a 1/4 to 3/8 inch expansion gap at every wall for a floating floor — but do not deduct it from the order. The gap is covered by the skirting, and planks still have to be cut to fit the full room width.
- 22 boxes cover 446.6 sq ft against 400 sq ft of floor, leaving 46.6 sq ft spare. Keep at least one unopened box: dye lots change, and a discontinued product cannot be matched for a later repair.
- Acclimatise the flooring in the room for the time the manufacturer specifies, usually 48 to 72 hours. Laying it straight off the truck is the most common cause of gapping and buckling later.
Boxes by layout pattern
The pattern decides the waste, and the waste decides the order.
| Layout | Waste | Area needed | Boxes |
|---|---|---|---|
| Straight, parallel to the long wall (yours) | 8% | 432 sq ft | 22 |
| Diagonal (45°) | 15% | 460 sq ft | 23 |
| Herringbone or chevron | 20% | 480 sq ft | 24 |
How much flooring do I need?
Multiply room length by width for the area, add 8% waste for a straight lay, then divide by the coverage printed on the box and round up. A 25 by 16 ft room needs 432 square feet, which is 22 boxes at 20.3 sq ft.
boxes = ⌈area × (1 + waste) ÷ coverage per box⌉- area
- Length × width in square feet
- waste
- 8% straight, 15% diagonal, 20% herringbone
- coverage
- Square feet per carton, printed on the box
The area is trivial; the two figures that decide the order are the waste factor and the box coverage, and both are routinely guessed. Waste is driven by the layout rather than by carelessness. A straight lay parallel to the long wall produces offcuts that can usually start the next row, so 8% covers it. A diagonal lay cuts every plank meeting the perimeter at an angle, and those offcuts rarely fit anywhere else, which pushes waste to around 15%. Herringbone is worse again at 20%. Box coverage varies by product from roughly 18 to 24 square feet, so using a round number instead of the figure on the carton can be out by a box either way. One thing not to do is deduct the expansion gap. A floating floor needs a quarter to three-eighths of an inch clear at every wall so it can move with humidity, but the planks still have to be cut to the full room width — the gap is hidden by the skirting, not saved from the order. Keep an unopened box afterwards: dye lots shift between production runs and discontinued products cannot be matched at all.
- Measure length and width at several points, taking the largest.
- Multiply them together for the floor area in square feet.
- Add waste according to the layout pattern you intend.
- Divide by the coverage printed on the carton.
- Round up to whole boxes and keep one spare unopened.
Worked example: A 25 × 16 ft room, straight lay, boxes covering 20.3 sq ft
A 25 × 16 ft room, straight lay, boxes covering 20.3 sq ft
The floor is 25 × 16 = 400 square feet. A straight lay parallel to the long wall needs about 8% for offcuts, giving 432 square feet to buy. At 20.3 square feet per carton that is 21.3 boxes, so you buy 22 — and those 22 boxes cover 446.6 square feet, leaving 46.6 square feet spare over the bare floor area. That spare is not surplus to discard: keeping one unopened box as attic stock is the only reliable way to repair a damaged plank years later, because dye lots shift between production runs. Changing the layout changes the order substantially. The same room laid diagonally needs 460 square feet and 23 boxes; herringbone needs 480 and 24. And note what does not change it — the quarter-inch expansion gap at the walls is covered by the skirting, so it never comes off the quantity.
What each flooring input means
- Room length
- Longest dimension of the room.
- Room width
- The other dimension. Measure at several points — rooms are rarely square, and the widest measurement is the one that matters.
- Coverage per box
- Printed on the carton and varies by product — 18 to 24 sq ft is typical for vinyl plank. Use the real figure rather than a round number.
- Layout pattern
- Diagonal and herringbone layouts cut every plank at the perimeter, which roughly doubles the waste against a straight lay.
- Additional waste
- Add more for an irregular room, many doorways, or a long plank in a short room where offcuts cannot be reused.
- Price per box
- Optional. Flooring is priced per box or per square foot — check which before comparing.
What this flooring does not account for
- Do not deduct the expansion gap. A floating floor needs a quarter to three-eighths of an inch at every wall, but planks are still cut to the full room width and the gap sits under the skirting.
- Box coverage varies by product from roughly 18 to 24 square feet. Use the figure on the carton rather than a round number, or the order can be out by a box.
- Measure the width at several points. Rooms are rarely square, and the largest measurement is what the planks must span.
- Keep one unopened box as attic stock. Dye lots change between production runs and a discontinued product cannot be matched at all.
- Acclimatise the flooring in the room for the manufacturer's stated period, usually 48 to 72 hours. Skipping it is the main cause of later gapping and buckling.
- Closets, bays and alcoves must be measured and added separately. A rectangle through the main room will miss them.
- Underlay is a separate purchase unless attached to the plank. Bathrooms and basements may also need a vapour barrier beneath it.
- Transition strips, reducers and stair nosing are priced per piece and are not included in a square-foot calculation.
Frequently asked questions
How much extra flooring should I buy for waste?
Eight percent for a straight lay, 15% for diagonal and 20% for herringbone. Add more for an irregular room or many doorways, where offcuts cannot be reused elsewhere.
How many boxes of flooring for a 400 square foot room?
Twenty-two boxes at 20.3 square feet each, allowing 8% waste for a straight lay. That comes to 446.6 square feet of coverage, leaving a useful margin for cuts and future repairs.
Do I subtract the expansion gap from my measurement?
No. The gap lets a floating floor move with humidity and is hidden by the skirting, but the planks are still cut to the full room width, so it never reduces the quantity needed.
Why does diagonal flooring need more material?
Because every plank meeting a wall is cut at an angle, and those angled offcuts rarely fit anywhere else. A straight lay produces offcuts that usually start the next row.
How long should flooring acclimate before installation?
Usually 48 to 72 hours in the room where it will be laid, though the manufacturer's instructions govern. Laying it immediately is the most common cause of gapping and buckling later.
Should I keep spare flooring?
Yes, at least one unopened box. Dye lots vary between production runs, so a later repair from a new batch will not match, and discontinued products cannot be sourced at all.
Sources and review
Last reviewed .