What a living room takes, carton by carton.

The biggest floor in the house, and the cheapest wall

A living room is usually the largest continuous floor you own and the largest continuous wall, which makes it the room where a ten percent decision costs the most and where a tin of paint changes the most for the least money. The sixteen by twelve room this page opens with, at a nine foot ceiling, is three purchases.

• The floor. Sixteen by twelve is 192 square feet. Adding the ten percent waste factor the Pergo project planner publishes gives 211, and at the 20 square feet per carton this page starts you at that is 10.56, so eleven cartons. Eleven cartons is 220 square feet delivered to cover 192.
• The walls. Two times sixteen plus twelve, times nine, is 504 square feet, less the 40 square feet of doors and windows assumed until you change it, so 464. Two coats is 928 square feet, and at the published 350 to 400 square feet per gallon both ends round up to three gallons.
• The sheets. Walls plus ceiling is 656 square feet. With ten percent for cuts that is 722, and a four by eight panel is 32 square feet, so 23 sheets. USG packs two to a bundle, so that is twelve bundles with one panel left over.

The accent wall costs a whole gallon

One wall a shade darker than the rest is the cheapest transformation in this room and the one most likely to be mispriced, because people estimate it as a fraction of the room and buy it as a whole container.

The long wall here is sixteen feet by nine, which is 144 square feet, and two coats is 288. That is comfortably inside one gallon at any point in the published range. But it is also comfortably above a quart, so a gallon is what leaves the store. The useful move is to run the calculator twice: once with the room as it is for the main colour, and once with the length and width of the single wall for the accent. Type sixteen in length, nine in width, and set coats to two. You get the accent wall on its own terms instead of guessing at a share of the whole.

The lines that are not square footage

The Pergo planner does not stop at cartons, and neither should a living room budget. It prints four more steps, and in a room this size three of them matter.

• Underlayment. Total square feet divided by the square feet per roll, and the planner's own printed example uses 100 per roll. So 192 square feet is two rolls. It also says plainly that if the floor you chose does not have underlayment attached, you need to buy one. Read the carton. If the pad is attached and it appears on your bill anyway, you are buying the same layer twice.
• Wall base or quarter round. Add the length and the width, multiply by two, then subtract the width of your doorways. Sixteen plus twelve is 28, doubled is 56 feet of perimeter, less a three foot doorway is 53 feet. That is sold by the stick, not by the foot, so it rounds up too.
• Transitions. The planner gives two divisors: doorway widths divided by 6.56 feet for 4-in-1 kits, or divided by 7.87 feet for individual transition sticks. Round up, and it recommends an extra piece for cutting errors. A living room usually opens onto two or three other rooms, so this line is rarely zero.

None of that appears in the carton count and all of it appears on the receipt.

If the room is on a slab

Ground floor living rooms are frequently over concrete, and the Pergo planner says in its own words that installing over concrete requires a vapour barrier. That is a subfloor question rather than a flooring question, which is exactly why it does not show up in any square footage calculation and why it surprises people. Find out what is under your carpet before you price anything, because the answer changes the shopping list and not the arithmetic.

The number that tells you what somebody else assumed

If a quote arrives with a carton count on it, you can now read the waste factor out of it in twenty seconds. Multiply their carton count by the square feet printed on the carton, then divide by your room. Fourteen cartons at 20 square feet is 280 square feet for a 192 square foot room, which is 1.46, a forty six percent waste factor against a published ten.

One honest thing has to be said in the other direction. Rounding up to a whole carton is worth several percent by itself and is nobody's fault, and a diagonal or herringbone layout genuinely takes more than a straight lay, which no manufacturer publishes a figure for. So compare before the rounding, and if the implied factor sits near 1.10 with one carton of rounding on top, the number is fine. If it sits at 1.4 with no diagonal in the conversation, ask what the extra is for and write the answer down.