How much flooring to order (and why 10% waste is not enough)

Every flooring guide tells you to add 10% for waste. It isn’t wrong so much as incomplete — it answers a smaller question than the one you asked. Ten per cent covers the offcuts. It doesn’t cover the box you’re forced to buy whole, and it doesn’t cover the plank you’ll want in three years when a chair leg goes through the finish.

Here’s how that number is actually built, using the specs our own catalogue records for the products we sell.

The three things people call “waste”

Three separate costs get bundled into one percentage, and they behave completely differently:

• Cut waste. The material that ends up in the bin: the ripped last row, the offcut at the end of each run, the piece you notch around a doorframe. This is the only one the 10% rule is really about.
• Box rounding. Flooring is sold by the carton. You can’t buy 10.8 boxes. On a small room this single constraint decides your waste percentage no matter what you planned.
• Attic stock. The spare box you keep. It isn’t waste at all — it’s insurance — but it comes out of the same budget, and it’s what surprises people at checkout.

Cut waste: what your plank width costs you

Of the 67,637 products in our catalogue that publish a width, the median is 7.8 inches. That figure does more work than it looks like it does, because the last row of a floor is almost never a whole plank.

Take a room 12 ft (3.66 m) wide, laid with 5.5 in planks. 144 in divided by 5.5 in is 26.18 rows. Twenty-six full rows cover 143 in and leave a 1 in strip at the wall — too narrow to click in, too narrow to look like anything but a mistake. What installers do instead is rip the first row as well, so both edges finish at about 3.25 in. You’ve now used 27 rows of material to cover 26.18 rows of floor: roughly 3% gone before you’ve cut a single doorway.

That’s one wall. Then add the ends of the runs:

• On a floating or click-lock floor the offcut from the end of one row usually starts the next — provided it’s longer than about 8 in (200 mm) and the locking profile isn’t directional. Some click systems only join one way, which halves how much of that offcut you can reuse.
• On a diagonal layout every row begins and ends on an angle, and almost nothing is reusable.
• In herringbone and chevron the offcuts come in mirrored pairs. Half of them fit nowhere.

Box rounding: the factor nobody budgets for

Say the product you’ve chosen lists 19.5 sq ft per box — check the coverage on the product page, because it varies a lot between lines. Now run two rooms through the same 10% rule.

Same product, same waste rule, wildly different outcome. Small rooms don’t get to choose their waste factor — the carton size chooses it for them. It’s also why splitting a house into “phases” costs more than doing it at once: every phase pays its own rounding.

Attic stock, and when to skip it

Add one full box, sealed, stored flat somewhere dry and indoors. On the 192 sq ft living room above that takes you from 11 boxes to 12 — 234 sq ft delivered against 192 sq ft of floor, about 22% over. That’s the honest total, and it’s roughly double the number most people budget.

It earns its place when:

• the line is clearance or run-out, where a re-order isn’t possible at any price;
• you’re a landlord, and one damaged plank otherwise means living with it or redoing the room;
• the floor is glued or nailed down, so a repair means matching, not swapping.

You can reasonably skip it when the product is a current, stocked line from a brand with depth behind it — we carry 419 brands, and they are not all equally likely to still list that colour in five years — and the space is small enough that you’d accept a slight batch difference on a later top-up. Dye lots do drift, so if you are topping up, match the batch or lot number printed on the carton label.

A waste factor that matches the layout

Cut waste isn’t a constant. Let the layout pick it:

Stairs deserve that last line. They’re cut and bought as individual pieces, and area arithmetic will mislead you every time.

Measuring: the part that actually goes wrong

1. Measure each rectangle separately and write it down. Don’t eyeball an L-shaped room as one number.
2. Include closets and doorway swings if the floor runs through them. It usually does.
3. Don’t subtract the footprint of a fridge, stove or dishwasher — the floor runs underneath.
4. Do subtract permanent built-ins that sit on the subfloor: a fixed island, a hearth, a tiled shower base.
5. Measure both diagonals of the room. If they differ by more than about 1 in the walls are out of square, the first row has to be tapered, and that’s extra material.
6. Add it all up, apply the layout allowance, divide by carton coverage, round up, then add the spare box. In that order.

The order that costs you the least

Order the whole job at once — floor, underlay, transitions, stair nosings, adhesive. Flooring moves by pallet, and a second shipment for two boxes of reducer costs a startling fraction of what the first shipment cost.

And know which end of the job you’re on. Across 2,000 sq ft, the difference between a padded 15% and a measured 9% is more than a hundred square feet of floor: measure properly instead of padding. Across a 60 sq ft bathroom, do the opposite — stop optimising, buy the extra box, get on with it.

Shop what this guide covers

• the full catalogue — every listing shows its coverage per carton, which is the number this whole article divides by.
• mouldings and trims — reducers, T-mouldings and stair nosings, counted in pieces rather than square feet.
• underlayment — bulky, light, and a whole second freight rating if it ships alone.
• wall base — quarter round and baseboard, priced by the linear foot.
• What flooring really costs to ship — why ordering the job in one go is the single biggest saving here.