Start with the room, not the square footage
A 400 sq ft living room is almost never a 20 by 20 square. The one we are working through here is 19 ft 6 in by 20 ft 6 in, which is 399.75 sq ft. That half foot matters, because laminate is bought in whole boxes and installed in whole rows, and both of those round in ways plain area math hides.
The box count is the easy half. The row layout is the half that ruins a Saturday.
The box formula
Boxes = round up ( room area x (1 + waste factor) / coverage per box )
Waste for a straight lay in a simple rectangular room runs about 7 percent. Coverage per box is printed on the carton and it is not standardized. Laminate cartons commonly land anywhere from 18 to 24 sq ft depending on plank thickness, width and how many boards the manufacturer stuffs in. Two products that look identical on the rack can be three boxes apart on the same floor.
For our room: 399.75 x 1.07 = 427.7, call it 428 sq ft of material needed.
| Coverage printed on the box | 428 sq ft divided by coverage | Boxes to buy | Actual material |
|---|---|---|---|
| 18.0 sq ft | 23.78 | 24 | 432.0 sq ft |
| 20.15 sq ft | 21.24 | 22 | 443.3 sq ft |
| 22.0 sq ft | 19.45 | 20 | 440.0 sq ft |
| 24.0 sq ft | 17.83 | 18 | 432.0 sq ft |
We will run the rest of this example on a common 12 mm plank, 7-1/2 in wide by 47-3/4 in long, 8 planks per carton, 20.15 sq ft per box. That is 22 boxes.
The first and last row problem
Here is what the box count does not tell you. Rows accumulate across the room in one direction, and the last row is whatever is left over. If that leftover is a sliver, the floor looks wrong and the sliver is a nightmare to click in.
Run the planks the long way, so the rows stack across the 19 ft 6 in dimension. That is 234 in. Take off the expansion gap at both walls, commonly 1/4 to 3/8 in for laminate, so 3/8 in each side:
234 – 0.75 = 233.25 in of floor to fill with 7.5 in rows
233.25 / 7.5 = 31.1 rows. So 31 full rows cover 232.5 in and the last row is 0.75 in wide. Three quarters of an inch. You cannot cut that, you cannot lock it, and even if you glued it in it would read as a mistake from the doorway.
The fix costs no extra material. Take one full plank width plus the leftover and split it between the first and last row:
(7.5 + 0.75) / 2 = 4.125 in
Rip the first row to 4-1/8 in, run 30 full rows in the field, and the last row also lands at 4-1/8 in. Check: (30 x 7.5) + 4.125 + 4.125 = 233.25. Same 32 rows, same material, two balanced edges instead of one ugly one.
The working rule is that no edge row should finish under about 2 in. Under that width the tongue or groove has almost nothing left to hold, the locking profile tends to break out during assembly, and the strip flexes underfoot. If your leftover comes out between 2 in and a full plank, leave it alone. If it comes out under 2 in, balance it.
Rows, planks and end cuts
Now the other direction. The room is 20 ft 6 in, or 246 in, minus the same 3/8 in at each end is 245.25 in of run per row. At 47-3/4 in per plank, that is 5 full planks (238.75 in) plus a 6-1/2 in end piece.
| Item | Number |
|---|---|
| Rows across the room | 32 (30 full width, 2 ripped to 4-1/8 in) |
| Full planks per row | 5 |
| End piece per row | 6-1/2 in |
| Planks in 22 boxes | 176 |
| Planks consumed if every row started fresh | 192 |
That second-to-last line is why offcut discipline matters. Straight through, 32 rows x 6 planks is 192 planks and you only bought 176. You close the gap by starting each new row with the offcut from the previous row. That also handles the stagger requirement, since most manufacturers want end joints in adjacent rows separated by a minimum distance, commonly 8 to 12 in. Check the sheet in the box for the number your product wants, because a 6-1/2 in offcut is below some minimums and cannot legally start a row under those instructions.
Transitions and the perimeter
A floating laminate floor needs a gap at every vertical obstruction, not just the four walls. That means door jambs, pipe penetrations, the fireplace hearth, and the island toe kick. Undercut the door jambs and casing with a jamb saw and slide the plank under, rather than scribing around them, and you get the gap and a clean line at the same time.
Doorways get a transition unless the same floor continues through. Measure each opening and order separately: a reducer where laminate meets something lower, a T-molding where the same floor continues but the run is broken, a stair nose at any drop. Nobody counts these until the floor is down.
What we would actually buy
Twenty-two boxes at 20.15 sq ft, plus one spare box set aside in the closet for future repairs. Laminate runs change, and a plank pulled from a box with the same run number three years from now will match. One pulled from a new run probably will not.
Let the material acclimate in the room before installation. Many manufacturers specify 48 to 72 hours with the boxes flat and the room at normal living temperature and humidity, and skipping it is a common warranty exclusion. Read the specific instructions in your carton, and if the room sits over a slab or a crawlspace, check what that product requires for moisture control before you open a single box.
Sources and Further Reading
Run your own numbers with the Flooring Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 7, 2026
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