Understanding your result
The headline is the cartons, with the area to order and the spare beside it. The table carries the usual chain from floor area through waste to cartons, and then adds the rows that belong to your installation method: underlayment rolls for a floating floor, adhesive and pails for a glue-down, or the linear run of plank for a nailed floor.
The carton arithmetic is the same as for the hardwood calculator: area times one plus the waste, divided by the carton coverage, rounded up. Engineered plank has little grade waste, so the allowance follows the layout alone: 10% straight, 15% diagonal, 20% herringbone.
For a floating floor the underlayment is counted at 5% over the area, which covers the trimming at the walls when the seams are butted; the underlayment calculator handles roll widths, seam tape and the vapor barrier in more detail. For a glue-down, the adhesive is the area divided by the coverage on the pail, with 10% for the ridges of adhesive that end up on the trowel and the rag; the coverage is typed in the pail’s own units (square feet per gallon or square metres per litre) because that is how it is printed. For a nailed floor the useful figure is the linear run of plank, which the cleats calculator turns into fasteners.
How we calculate this
The waste percentages are the layout figures on the waste factors reference. The adhesive coverage default, 45 sq ft per gallon, is the middle of the 40 to 60 that the common urethane adhesives (Bostik, Sika, Roberts) print for the trowel they specify; a moisture-barrier adhesive laid at full depth is at the bottom of that range or below it. The underlayment guide covers what goes under a floating floor and when a vapor barrier is needed, and the expansion gaps guide explains why a floating floor needs room at the walls and a break in long runs.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Carton coverage | 22 sq ft (2 m²) | Engineered plank cartons run 18 to 30 sq ft (manufacturer product pages, 2025); the label is the figure to use |
| Plank width | 5 in (12.5 cm) | The most common engineered width; 7 in and wider are increasingly common |
| Waste | 10 / 15 / 20% by layout | Industry rule of thumb, see the waste factors page |
| Underlayment allowance | 5% | Trimming at the walls with butted seams; 10% if the product overlaps |
| Adhesive coverage | 45 sq ft per gallon (1.1 m² per L) | Mid-range of urethane wood adhesive technical data sheets with the specified trowel |
| Adhesive allowance | 10% | Adhesive left on the trowel and in the pail; manufacturer installation guidance |
| Pail | 3.5 gal (15 L) | Common pail sizes for wood flooring adhesive |
Assumptions last reviewed October 8, 2026.
The calculator does not count the moisture test, the primer some adhesives need on a slab, the transition strips at doorways or the expansion gap itself; the expansion gap calculator gives the gap and the run limits for engineered wood. For a nailed floor it gives the linear run only; the fastener count and the rosin paper are separate calculators. It treats the plank width as the nominal width and the room as its area alone.
Two worked examples
A 20 × 15 ft family room, floating
24.5 sq ft cartons at $110, straight layout, 100 sq ft underlayment rolls.
- Floor area: 20 × 15 = 300 sq ft; with 10%: 330 sq ft
- Cartons: 330 ÷ 24.5 = 13.5, rounded up to 14 cartons (343 sq ft), $1,540
- Spare: 43 sq ft
- Underlayment: 300 × 1.05 = 315 sq ft ÷ 100 = 3.15, rounded up to 4 rolls
Four rolls of underlayment for 315 sq ft leaves most of a roll over; a 200 sq ft roll and a 100 sq ft roll would do it with less left. The 43 sq ft spare is almost two cartons, one of which is worth keeping.
350 sq ft of 7 in plank, glued to a slab
26 sq ft cartons, adhesive at 50 sq ft per gallon in 4 gallon pails.
- Area to order: 350 × 1.10 = 385 sq ft
- Cartons: 385 ÷ 26 = 14.8, rounded up to 15 cartons (390 sq ft)
- Adhesive: 350 ÷ 50 = 7.0 gallons; with 10%: 7.7 gallons ÷ 4 = 1.9, rounded up to 2 pails
Two pails, and not much to spare. If the slab needs a moisture-barrier adhesive at its deeper trowel, the coverage drops to around 35 sq ft per gallon and the order becomes three pails; the pail’s data sheet, not the default here, is the figure to trust once you know the product.
Where to find your inputs
Carton coverage. On the carton and the product page. Engineered cartons vary more than solid strip, so do not assume 20 sq ft.
Installation method. The product page says which methods the plank is rated for; many are rated for all three. Over concrete, float or glue; over plywood, any.
Adhesive coverage. On the pail’s data sheet as square feet per gallon for a named trowel. Use the trowel named, or the coverage figure means nothing.
Underlayment roll coverage. On the roll: 100 or 200 sq ft for foam and felt.
Common mistakes
- Underlayment under a glued floor. Glue bonds to the subfloor; nothing goes between. Underlayment is for floating floors only.
- Reading the adhesive coverage without the trowel. A bigger notch halves the coverage. The coverage and the trowel go together.
- No vapor barrier over a slab. A floating floor over concrete needs one; a glue-down needs a moisture test and probably a barrier adhesive.
- Forgetting the expansion gap. A floating floor pinned by a baseboard or a cabinet buckles in summer.
- Herringbone from ordinary cartons. Pattern products with fixed lengths exist for a reason; random lengths waste far more than 20%.
- Mixing methods in one room. A floor part glued and part floating cracks where they meet. Choose one.
Questions people ask
- How many cartons of engineered wood for 400 square feet?
- With a 22 sq ft carton and 10% waste for a straight layout, 400 sq ft becomes 440 sq ft, which is exactly 20 cartons. A 24.5 sq ft carton needs 18; a diagonal layout at 15% with the 22 sq ft carton needs 21.
- How much adhesive does a glue-down wood floor need?
- Urethane wood flooring adhesives spread about 40 to 60 sq ft per gallon with the trowel the pail specifies, so a 350 sq ft room at 50 sq ft per gallon needs 7 gallons, or two 4 gallon pails with the usual 10% allowance. A moisture-barrier adhesive applied thicker can halve the coverage.
- Does engineered flooring need underlayment?
- A floating engineered floor does, unless the planks have an attached pad. It takes a foam or felt underlayment, with a vapor barrier over concrete. A glued or nailed engineered floor does not; the adhesive or the fasteners hold it to the subfloor directly, though a nailed floor over plywood is usually laid over rosin paper.
- What waste factor for engineered wood?
- 10% for a straight layout, 15% for a diagonal, 20% for herringbone, the same as laminate and vinyl plank. Engineered boards come in fixed lengths with few defects, so grade matters less than it does for solid wood; the cuts at the walls are most of the waste.
- Can I float engineered wood over concrete?
- Yes, and it is the usual way to put wood on a slab, with a 6 mil vapor barrier or a combined underlayment, the planks clicked or edge-glued, and an expansion gap all round. Glue-down over concrete is also common but needs a moisture test and often a moisture-mitigating adhesive. Nailing into concrete is not an option.
- Which installation method is cheapest?
- Floating is cheapest in labour and needs the least equipment; glue-down costs more in adhesive and time; nailing needs a flooring nailer and a wood subfloor. Over a sound plywood floor, nailing is often quickest for a pro and floating easiest for a first-timer. The installer labour cost calculator has the ranges.