A 15 x 12 ft living room is 180 sq ft. With a 10% cutting allowance you need to cover 198 sq ft, which is 9 cartons of 22.5 sq ft - about 4 sq ft to spare.
Result
Floor area180 ft²
Waste allowance10%
Including offcuts198 ft²
Packs9
Packs cover202.5 ft²
Left over4.5 ft²
Assumptions used
0.1 fraction – Laminate installation guides: RW Supply + Design (2023) add up to 10% straight, 18% diagonal; Egger: average 5% offcut in rectangular rooms (2026-10-10)
How the number is worked out
The floor area is length times width; an L-shaped room is two rectangles added
together. The cutting allowance is added to that area, and the result is divided
by the coverage printed on one carton and rounded up. A store will not split a
carton, so the last one is always whole, and the square feet left over are shown
so you can see what the rounding cost.
Straight or diagonal
Laid parallel to the walls, the offcut from the end of one row usually starts
the next, so waste stays low. Laid at 45 degrees, every board along the walls is
cut at an angle and the triangle that falls off rarely fits anywhere else. That
is why the diagonal allowance is almost double.
What is not included
Underlayment, transition strips and baseboard are sold separately and by
different units - rolls, lengths, pieces. The expansion gap at the walls is not
subtracted either: it is a few millimetres wide, the baseboard covers it, and
leaving it in errs on the side of one carton too many rather than one too few.
Worked example
Living room, 15 × 12 ft, cartons of 22.5 sq ft
Floor area
180 ft²
Including offcuts
198 ft²
Packs
9
Left over
4.5 ft²
Calculated by materiacalc using the same engine that runs the tool above.
In this market
Flooring cartons in the US are labelled with the square feet they cover, and that figure differs between plank widths of the same product line. Read it off the carton you are actually buying rather than the product page.
Questions
How much extra laminate should I buy?
About 10% for a straight lay and 18% on the diagonal, which is what manufacturers' installation guides recommend. A plain rectangular room can come in nearer 5%; a room with alcoves and doorways needs the full allowance.
Why enter the carton's square feet and not the plank size?
Because cartons are sold by coverage. The planks inside are cut to fit the room, so the figure printed on the carton is the one that decides how many to buy.
Should I keep the leftover planks?
Yes. A damaged board can be swapped out years later, but only from the same product, and flooring lines are discontinued often.