Waste factors follow NWFA guidance. Extras are added below.
Room 1
Tread, riser and nosing together.
Advanced options
Printed on the box. Usually 18–24 ft².
Used for the last-row check.
Adds to the waste factor.
This flooring calculator works out how many cartons to buy — not square feet — with the waste factors compounded properly and a check on whether your last row will come out too narrow to install.
The short answer
Floor area × waste factor ÷ coverage per carton, rounded up. A 20 × 14 ft room at 280 ft² with 10% waste needs 308 ft², which at 20 ft² per carton is 16 cartons.
Flooring is sold by the carton and is dye-lot specific, so always buy one spare box — a replacement bought in two years won’t match.
On this page
How to use this flooring calculator
Pick your installation pattern, enter the space, and the calculator returns cartons with the waste already built in. Four modes:
- Room — a rectangle, and the mode that runs the last-row check
- L-shape — overall dimensions minus a cut-out
- Stairs — treads counted at their real material use
- Known area — you’ve already measured
Flooring several rooms in the same product? Use Add another room and the calculator totals them into one order. That matters more here than on most jobs, because everything needs to come from the same dye lot.
Under Advanced options: carton coverage, plank width, room complexity, whether you’re a first-time installer, underlayment and price.
The flooring formula
1. Area = Length × Width
2. Material = Area × (1 + waste %)
3. Cartons = Material ÷ coverage per carton, rounded up
You cannot buy half a carton — always round up, and check what
the rounding leaves you as a spare.
Worked example — 20 × 14 ft room, straight lay, 7 in planks
Two cartons spare is a good outcome — enough for future repairs from the same dye lot.
Waste factors compound — they don’t replace each other
Most calculators ask you to pick one waste percentage. But the things that cause waste stack: a herringbone pattern in wide planks, in a room full of closets, installed by someone doing it for the first time, wastes far more than any single figure captures.
| Factor | Adds | Why |
|---|---|---|
| Straight lay | 10% | Base — off-cuts start the next row, so most is reused |
| Diagonal 45° | 15% | Every perimeter piece is an angled cut with an unusable off-cut |
| Herringbone or chevron | 18% | High cut ratio throughout the field, not just at edges |
| Wide planks, 7 in or more | +3% | Bigger drop pieces that often can’t be reused |
| Moderate complexity — closets, doorways | +3% | More starts and stops |
| High complexity — many angles, alcoves | +5% | Every direction change costs a cut |
| First-time DIY installer | +2% | Learning-curve cuts and a few ruined planks |
| Stairs included | +2% | Nosing cuts are unforgiving |
So a herringbone floor in 8 inch planks, in a room with closets, laid by a first-timer, comes to 18 + 3 + 3 + 2 = 26%, not 18%. That difference is two extra cartons on a 400 ft² room — and running short mid-install is far worse than having spare.
The National Wood Flooring Association publishes 7–10% for straight installations, 12–15% for diagonal and 18–20% for herringbone or chevron. This calculator uses the upper end of straight lay and the lower end of herringbone as the base, then adds the specific factors above rather than asking you to guess where in the range you fall.
The last-row problem
This is the detail that separates a floor that looks right from one that doesn’t, and no other flooring calculator checks it.
Plank flooring runs in rows. Divide the room width by the plank width and you rarely get a whole number — there’s a remainder, and that remainder is the width of your final row. If it comes out under about two inches, you have a problem:
- A sliver that narrow is fragile and often snaps while you’re cutting it
- Click-lock planks that narrow are very hard to engage in the last row against a wall
- It looks wrong — a hairline strip along one wall against full planks on the other
Trim width = (Plank width + Last row width) ÷ 2
13 ft room, 7 in planks → 22 full rows + a 2.00 in last row
Rip the first row to (7 + 2) ÷ 2 = 4.5 in
Now the first and last rows are both 4.5 in and it looks deliberate.
You rip the first row, not the last, because the first row sits against a wall where the cut edge is hidden by baseboard, and because you have to make the decision before you start — by the time you reach the far wall it’s too late.
The calculator runs this check automatically for a single rectangular room and tells you the trim width if you need one.
Buying by the carton
Flooring is priced per square foot but sold by the carton, and you can’t buy part of one. That rounding is not waste — it’s your spare stock, and it matters.
| Material | Typical carton coverage |
|---|---|
| Luxury vinyl plank (LVP / SPC) | 18–24 ft² |
| Laminate | 15–30 ft² |
| Engineered hardwood | 20–25 ft² |
| Solid hardwood bundles | 18–25 ft² |
| Porcelain and ceramic tile | 10–18 ft² |
Carton coverage varies enormously — laminate alone ranges from 15 to 30 ft² per box. At 320 ft² of material, that’s the difference between 11 cartons and 22. Every product page and every box lists the actual figure. Put that number into the calculator rather than accepting the default.
Dye lots, and why you buy a spare box
Flooring is manufactured in production runs. Colour, gloss and embossing vary subtly between runs — not enough to notice in the store, very much enough to notice as a patch in the middle of a floor.
Two years after installation, a dropped pan, a pet or a furniture leg damages a plank. If you have a spare box from the original lot, it’s a twenty-minute repair. If you don’t, your options are a visible mismatch, or lifting and replacing the floor.
Do
Buy it all at once
One order, one dye lot. If you’re doing several rooms over time, buy the material for all of them now.
Do
Keep a sealed box
Store one unopened carton flat and dry. It’s the cheapest insurance in the whole project.
Don’t
Rely on reordering
LVP and laminate lines are reformulated and discontinued constantly. “Close enough” isn’t, on a floor.
Cartons by room size
Straight lay, 10% waste, 20 ft² cartons.
| Room | Area | With waste | Cartons | Spare |
|---|---|---|---|---|
| 10 × 10 ft | 100 ft² | 110 ft² | 6 | 20 ft² |
| 12 × 12 ft | 144 ft² | 158 ft² | 8 | 16 ft² |
| 12 × 14 ft | 168 ft² | 185 ft² | 10 | 32 ft² |
| 14 × 20 ft | 280 ft² | 308 ft² | 16 | 40 ft² |
| 16 × 20 ft | 320 ft² | 352 ft² | 18 | 40 ft² |
| 20 × 20 ft | 400 ft² | 440 ft² | 23 | 60 ft² |
| 20 × 24 ft | 480 ft² | 528 ft² | 27 | 60 ft² |
Which material?
| Material | Cost per ft² | Strengths | Watch out for |
|---|---|---|---|
| Laminate | $1–$4 | Cheapest, scratch resistant, easy click-lock | Water damages the core permanently |
| LVP / SPC | $2–$5 | Fully waterproof, DIY friendly, quiet underfoot | Softer surface, can dent under heavy furniture |
| Engineered hardwood | $4–$10 | Real wood surface, stable over concrete | Thin wear layer limits refinishing |
| Solid hardwood | $6–$15 | Refinishable many times, adds resale value | Needs acclimation; not for basements or wet areas |
| Tile | $2–$10 | Fully waterproof, extremely durable | Hard, cold, needs a flat and rigid subfloor |
Professional installation typically adds $2–$5 per square foot on top of materials.
Stairs
Stairs consume far more material per step than the tread area suggests, because each step needs a tread, a riser and a nosing — and every one is a cut. Budget about 12 square feet per tread, so a standard 14-step flight is around 168 ft².
Order stair material from the same dye lot as the adjoining floor. A staircase connecting two floors in slightly different shades is one of the more visible mistakes you can make, and it’s not fixable without redoing it.
Underlayment
Floating floors — laminate, LVP, engineered click-lock — usually need underlayment for cushioning, sound and moisture control. Rolls typically cover 100 ft², so a 280 ft² room takes 3 rolls.
- Check whether it’s pre-attached. Many LVP and laminate products have a pad bonded to the underside. Adding a second layer makes the floor spongy and can void the warranty.
- Over concrete, use a moisture barrier — a 6 mil vapour retarder or an underlayment with one built in.
- Nail-down solid hardwood uses rosin paper or felt, not foam underlayment.
- Follow the flooring manufacturer’s spec. They specify the approved type, and using the wrong one can void the warranty.
Flooring ordering mistakes to avoid
- Ordering exactly what the calculator says. Add a spare carton — dye lots don’t come back.
- Using a generic carton coverage. It ranges from 15 to 30 ft²; use the number on your box.
- Picking one waste factor. Pattern, plank width, room complexity and skill all stack.
- Ignoring the last row. A one-inch sliver along a wall can’t be undone after the fact.
- Buying in two orders. Different lots show as a line across the floor.
- Doubling up underlayment on planks that already have it attached.
- Skipping acclimation on hardwood — 48 to 72 hours in the room before installing.
Frequently asked questions
How much flooring do I need?
Multiply length by width for the area, add your waste factor, then divide by the coverage printed on the carton and round up. A 20 × 14 ft room is 280 ft²; at 10% waste that’s 308 ft², which is 16 cartons at 20 ft² each.
How much extra flooring should I order?
10% for straight lay, 15% for diagonal and 18–20% for herringbone, per NWFA guidance. Add roughly 3% for planks 7 inches or wider, 3–5% for rooms with many closets or angles, and 2% if it’s your first install. These stack rather than replacing one another.
How many square feet is a box of flooring?
Typically 18–24 ft² for LVP, 15–30 ft² for laminate, 20–25 ft² for engineered hardwood and 10–18 ft² for tile. The range is wide enough that using an average will give you the wrong carton count — take the figure from your product’s box.
What if my last row is too narrow?
Rip the first row narrower so the first and last rows match. Take the plank width plus the last row width and halve it — a 7 inch plank with a 2 inch last row means cutting the first row to 4.5 inches. Rows under about 2 inches are fragile, hard to click in and look wrong.
Should I buy an extra box of flooring?
Yes, always. Flooring is dye-lot specific and products are regularly reformulated or discontinued. A spare carton from the original lot turns a future damaged plank into a twenty-minute repair instead of a visible mismatch or a whole new floor.
How much flooring for a 12×12 room?
144 square feet, which at 10% waste is 158 ft² — 8 cartons at 20 ft² each, supplying 160 ft². That leaves only 16 ft² spare, so consider a ninth carton for future repairs.
How much flooring do stairs use?
About 12 square feet per tread once you count the tread, riser and nosing — so a 14-step flight needs around 168 ft². Order stair material from the same dye lot as the floor it connects to.
Do I need underlayment?
Floating floors usually do, unless the planks have a pad pre-attached — check the packaging, because doubling up makes the floor spongy and can void the warranty. Over concrete you also need a moisture barrier. Nail-down solid hardwood uses rosin paper or felt instead.
How do I calculate flooring for an L-shaped room?
Use the L-shape mode, which takes the overall rectangle and subtracts the cut-out. For more complex shapes, split the space into rectangles and add each as a separate area — the calculator totals them into one carton count.
Does diagonal flooring really waste more?
Yes. In a straight lay the off-cut from the end of one row starts the next, so most material is reused. Cut a plank at 45 degrees and the off-cut is an angled piece that only fits the opposite corner. That’s why diagonal runs 15% against straight lay’s 10%.
Which flooring is cheapest?
Laminate at $1–$4 per square foot, followed by LVP at $2–$5. Both are click-lock and DIY friendly. Engineered hardwood runs $4–$10 and solid hardwood $6–$15. Professional installation adds $2–$5 per square foot on top.
Can I use this flooring calculator in metric?
Yes. Switch the header toggle from Feet to Metres for room dimensions. Carton coverage and areas are shown in square feet — multiply square feet by 0.0929 for square metres.
Sources and method
- National Wood Flooring Association installation guidelines — waste allowances by pattern
- Manufacturer installation instructions for carton coverage, acclimation and underlayment requirements
- Additional waste factors for plank width, room complexity and installer experience reflect published trade guidance
- Coverage on any specific product should be taken from the carton, which varies substantially by product
Related calculators
Tile CalculatorTile count by size and pattern
Paint CalculatorWalls, ceiling and primer
Drywall CalculatorSheets, screws and compound
Baseboard CalculatorLinear feet and lengths to buy
Concrete Slab CalculatorIf you’re starting from the subfloor
How this flooring calculator works out its numbers
Floor area is calculated from your dimensions, then multiplied by a compound waste factor: a base rate by pattern, plus additions for plank width, room complexity, installer experience and stairs. These add rather than replacing one another, because each describes a different source of off-cut. Cartons are the resulting material divided by your carton coverage, rounded up, with the surplus reported so you can see how much spare stock the rounding leaves.
The last-row check divides room width by plank width, takes the remainder as the final row, and flags anything under 2 inches. Where a trim is needed, the recommended first-row width is the average of the plank width and the last-row width, which balances both edges. This check applies to a single rectangular room, since the geometry of multi-room and irregular layouts depends on which direction you run the planks.
Waste percentages are planning figures based on NWFA guidance. Carton coverage should always come from your actual product — it ranges from 15 to 30 ft² and is the input with the largest effect on the result.