Flooring calculator

The arithmetic

Floor area, plus a percentage for waste, divided by what one box covers, rounded up. The rounding up is the whole point: a shop sells boxes, not square feet, and 11.2 boxes is 12 boxes.

The waste is added to what you order, never to the floor you measured. Your room does not get bigger because you chose a diagonal.

How much waste the pattern really costs

A diagonal lay wastes a triangle at every wall. Herringbone wastes two cuts on every piece, so it is the most expensive pattern to lay before you have paid for a single extra plank.

Two things are worth knowing about these numbers. The manufacturers disagree with each other about a diagonal, and one of them disagrees with itself: Mullican’s sheet says to add 5% in its advice line and 5–7% in its own worked formula. And Havwoods drops its allowance for big floors — 7% instead of 10% for plank, 12% instead of 15% for herringbone, once the floor is over 100 m² — because the offcuts from one room get used in the next.

Box coverage is the number to check

It is printed on the carton and it varies by a third between products. A Pergo Outlast+ laminate box covers 19.63 sq ft; a Shaw Homebound vinyl plank box covers 23.89. Getting it wrong by that much is getting your order wrong by two boxes on a small room, so the field starts at the laminate figure and expects you to correct it.

Underlayment

Underlayment is rolled out over the floor rather than cut around a pattern, so the plank waste percentage does not apply to it — this page counts rolls against the area you measured. Rolls come in 100 sq ft and 450 sq ft in the US, and 10 m² and 15 m² packs in the UK.

Leave the field empty if your planks have a pad already attached, which most laminate does.

The plank layout and its cut list

For a straight lay, the page also lays each rectangular room plank by plank, the way the makers’ instructions lay it, and draws it with every cut piece shaded. The cut list gives each row: how wide it is, the piece it starts with, the whole planks, the piece it ends with, and where each piece comes from. The planks it takes are the waste for your room worked out rather than guessed, and the page sets the boxes they fill beside the order by area.

The rules come from the makers, by the kind of floor, and every figure can be typed over with the one in your box:

The makers do not agree: Mohawk asks for end joints 6 in apart, Lifeproof 8 in, Shaw 12 in and Kährs 500 mm. So each kind of floor takes one maker’s whole set, and a second maker fills in only where the first says nothing. Kährs widens its gap by 1.5 mm for every metre across the floor, so a room more than 6.7 m wide gets more than 10 mm, and the page shows each room’s own gap.

How a row is laid:

• Rows run along the room, or across it if you tick the box. When the last row would be narrower than the rule, the first is trimmed too, so the two match. Kährs: “If it is less than 30 mm wide, you should also saw the first row of boards”.
• Each row starts with an offcut from the end of an earlier row when that keeps the rules. Shaw: “Use a cut piece of board from the previous row to start the next row.” Otherwise it starts with a whole plank, or one cut shorter a stagger at a time.
• A cut piece can only go one way. Only one end of it is the factory’s, so the piece left from starting a row can only end one, and the piece left from ending a row can only start one. Lifeproof, on the piece left from starting a row: “The remaining piece can then be used on the opposite side of the room, at the end of that row”.
• Alternate rows are kept from lining up where that costs no plank. The NWFA says to “Avoid “H” patterns when possible.”

When the rules cannot all be kept, the page says so instead of hiding it. End joints 12 in apart cannot be kept on a 22 in plank, for example, because no two starts on it are more than 11 in apart. The page then counts the rows that miss and says how close they come.