Flooring, decking and wallpaper calculator
Divide the area by the coverage of one unit, then add for cuts. A 5 × 4 m room is 20 m²; at 1.97 m² a pack that is twelve packs after 10% waste. The same panel counts deck boards with their drainage gap and wallpaper rolls with the pattern repeat, and works grout out from the tile size and the joint rather than from the area alone: 30 cm tiles at a 3 mm joint 8 mm deep come to 0.256 kg per m², so a 12 m² floor takes 3.07 kg and one 5 kg bag.
How to work out flooring
Two details cost more than the cutting waste on a floor. The first is that the last row is almost never a full plank width, and if it works out under 50 mm the whole floor should be shifted so the first and last rows are balanced, which costs one extra row of material. The second is expansion gap: floating floors need 10–12 mm all round, hidden by beading but not optional. Butting a laminate floor tight to the skirting is the single most common cause of a floor that buckles in summer.
Decking counts the same way with one change: the drainage gap belongs to the board. Timber needs 5 to 6 mm between boards so water drains and the wood can move, so the honest coverage of a 150 mm board is 155 mm. Board count is the easy half in any case — the joists underneath are where a deck succeeds or fails. Four hundred millimetre centres for standard timber, dropping to 300 mm for a diagonal lay or for most composite, which is less stiff than wood. Two screws per board per joist means a 12 m² deck is comfortably 400 fixings.
Wallpaper is the one place where deducting openings loses you money. A standard door removes about 1.8 m² of wall, but it interrupts two drops, and the offcuts above and below it are rarely long enough to reuse, so the deduction and the extra waste cancel out. The exception is a room that is mostly glass; a wall of patio doors genuinely is not being papered. The waste figure itself is set by the pattern: a free-match paper wastes only the trim, while a straight match with a 32 cm repeat can lose a third of a metre on every drop.
Grout is the odd one out, because the joint is a three-dimensional trench rather than a surface. Its volume is the length of joint per square metre times the joint width times the tile depth, so halving the tile size doubles the joint length, doubling the joint width doubles it again, and a 20 mm porcelain plank has three times the joint depth of a 6 mm ceramic wall tile. Work it through and 30 cm tiles at a 3 mm joint 8 mm deep come to 0.256 kg per square metre; 60 cm tiles at the same joint are exactly half that, 0.128 kg, because doubling the tile halves the joint length. A 25 mm mosaic has twelve times the joint length of the 30 cm tile and usually sits on a 4 mm bed rather than an 8 mm one, so it lands at 1.536 kg, six times as much. Those three figures are the whole reason a single bag-per-square-metre rule is wrong for every tile but the one it was written for, and the reason the grout mode here derives the rate from the tile you enter instead of printing a constant.
What people use it for
- Ordering laminate or engineered board for a room
- Costing luxury vinyl tile by the pack
- Comparing plank sizes for the same room
- Adding up several rooms on one order
- Counting deck boards for a garden deck
- Comparing timber against composite for the same deck footprint
- Working out wallpaper rolls including the pattern repeat
- Ordering paper for a single feature wall
- Buying grout with the tiles rather than making a second trip
- Costing a regrout of a floor that is already tiled
- Judging a mosaic job, where the tile count per square metre is many times higher
- Costing a deck by the board before committing to the build
- Working from an American roll size rather than a European one
- Checking a decorator’s roll count or a tiler’s tile count against your own
Questions
Ten per cent for a straight lay in a simple room. Fifteen if the room has bays, alcoves or a diagonal lay; twenty for herringbone.
Yes. 10 to 12 mm around every edge and around pipes, for any floating floor. It is covered by beading or skirting and it is not optional.
Typically 1.8 to 2.2 m². It is printed on the pack, and it is the only number that really matters for the count.
Buy it to the room area plus a small margin, not to the plank count. Some laminates have underlay pre-attached, in which case you need none.
Usually yes for a floating floor, provided the tiles are sound and level. Check the door clearance first, because the build-up can stop a door closing.
Five to six millimetres for timber, which allows drainage and movement. Composite expands more with temperature, so its makers specify their own gap and it is usually wider at the ends.
400 mm centres for boards running perpendicular, 300 mm for a diagonal lay or for most composite boards.
A standard European roll of 10.05 × 0.53 m covers 5.33 m². American rolls are usually 8.2 m by 0.686 m, about 5.6 m².
Generally no. The offcuts around them are rarely reusable, and the deduction usually cancels out against the extra waste.
The batch number is the print run code on the label, and rolls from different runs differ noticeably in colour. Buy them together and check the numbers match. Topping up later is a gamble: patterns get discontinued and batches sell out, and one spare roll costs far less than restarting a wall.
0.256 kg for 30 cm tiles at a 3 mm joint, 8 mm deep. Double the tile to 60 cm and it halves to 0.128 kg. A 25 mm mosaic on a 4 mm bed at the same joint width is 1.536 kg, six times as much. Change the tile size in the panel and the rate changes with it.
The panel rounds it up for you against the bag size you pick, since grout comes in 2.5, 5 and 20 kg. A 12 m² floor of 30 cm tiles needs 3.07 kg, so one 5 kg bag. Buy the whole job in one go, because colour varies between batches.
Directly and proportionally. Going from a 2 mm to a 4 mm joint doubles the grout.
Floor grout is usually sanded for joints over 3 mm and is harder wearing. Unsanded grout suits narrow joints and polished tiles it might otherwise scratch.
Not usually. Adhesive needs 24 hours to cure, and grouting into soft adhesive traps moisture and causes patchy colour.
Twenty to thirty minutes. Once it stiffens, slackening it with more water costs you both strength and colour consistency, so mix what you can lay in that window and no more.