How do I stop the last row of flooring being a thin sliver?

The width calculation that takes five minutes before you start, and the first-row rip that makes both edges of the room match.

Difficulty: intermediate
Time: 45 min
Read: 5 min

Short answer

Measure the room width, subtract both expansion gaps, divide by the board width, and look at the remainder. If it comes out less than about half a board, rip the first row narrower so the first and last rows are equal and both are comfortably wide. Measure at both ends of the room, because the walls are rarely parallel.

The last row is where a floating floor job goes wrong for people who did everything else right. A very narrow final strip will not hold its click joint, cannot be gripped to tap home, and looks like an accident. Five minutes of arithmetic before the first board goes down removes the problem entirely.

What you'll need

tape measure and calculator
a saw that can rip lengthways — circular saw, table saw or jigsaw
a straight edge or guide for the rip
spacers for the expansion gap
a pencil and a scribing block (optional)

Setting a floating floor out across its width so the last row is not a sliver

Step by step

Measure the room's width at both ends and in the middle.Across the direction the boards will run. Note all three figures; the difference between them is what you have to accommodate in the first-row scribe.
Subtract the expansion gap at both walls.The gap is not optional. The flooring manufacturer states the size; use theirs, and take it off both sides of the width before dividing.
Divide by the covering width of a board.The covering width, not the overall width — the tongue that disappears into the previous board does not count. It is printed on the pack or measurable off a joined pair.
Look at the remainder.That is the width of the last row exactly as it will be if you start with a full board. If it is more than about half a board, you can start with full boards and stop worrying.
If the remainder is small, split the difference with the first row.Add the remainder to one full board width and halve it. Rip the first row to that width, and the last row comes out the same. Both edges of the room now have a comfortable board and they match.
Check what happens under the door and against the fitted furniture.The width you chose may put a joint in an awkward place at a threshold or under a kitchen plinth. It is easier to adjust now.
Scribe the first row rather than ripping it straight, if the wall is not straight.Lay the first row loose against the wall with spacers, run a block and pencil along the wall to transfer its shape onto the board, then cut to that line. The floor is now square even though the wall is not.
Rip with the decorative face up or down depending on the saw.Laminate chips on the side where the teeth exit. A circular saw cuts upwards, so cut face down; a handsaw or jigsaw with a downcut blade differs. Test on an offcut.
Keep the expansion gap all the way round as you lay.Spacers against every wall and every fixed obstacle, left in until the beading or skirting goes on.
Apply the same rule to the length of each row.Never finish a row with an end piece shorter than about 300mm, for the same reason: it will not hold.

Tips

The first row is also the row that sets the whole floor's straightness. Time spent on it is repaid across the entire room.
If a rip cut is only a few millimetres, it can be planed or belt-sanded off rather than sawn — a very narrow rip is hard to cut safely.
In a room with a chimney breast or a bay, work the width calculation to the widest part and check the alcoves separately.
Dry-lay two or three rows before fixing anything at all. Cheap insurance.

Common mistakes

Starting with a full board and hoping — The last row's width is then whatever is left, and there is roughly an even chance it is unworkably narrow. A sliver will not lock into the previous row's click profile, so it lifts and rocks, and it is the row right against the most-used edge of the room.
Measuring the room at one point only — Opposite walls are rarely parallel. A room that is 3.60m at one end and 3.57m at the other will produce a last row that tapers, and if you set out from the wide end the narrow end may end up impossibly thin.
Forgetting the expansion gap in the calculation — The gap is a real part of the room width — often 10mm or more at each side. Leaving it out of the arithmetic makes the last row wider on paper than it turns out to be in practice.

If it doesn't work

The last row is 20mm wide and will not stay down

Cause: No width setting-out before starting — Fix: The honest options are to lift and re-lay from a ripped first row, or to glue the sliver down and accept it. Gluing pins the raft, so it is a compromise rather than a fix.

The last row tapers from 90mm to 40mm

Cause: Walls not parallel and the first row laid straight — Fix: Scribe the first row to the opposite wall instead, so the taper is split between the two sides where it is less noticeable.

The first row will not stay tight to the wall as you work

Cause: Nothing holding it while the next rows are engaged — Fix: Use spacers as wedges against the wall, or temporarily screw a batten outside the expansion gap to work against.

Questions people ask

Which row should I rip — the first or the last?

The first. It is against a wall you can scribe to, it is done while you have most room to work, and ripping it means the last row — the one you have least access to and have to lever into place — is a comfortable width.

How wide is comfortable for a final row?

There is no single number, but the practical test is whether the board can hold a click joint and be gripped or levered without breaking. Manufacturers often give a minimum, and roughly a third to a half of a board width is the region where people stop having trouble.

Does this apply to LVT and vinyl planks too?

The width arithmetic applies to any plank floor. For glue-down products a narrow final strip is much less of a problem structurally, since it is stuck rather than clicked, but it still looks better to balance the two edges.