Flooring calculator
Packs to order for laminate, vinyl plank, engineered or solid wood — plus the last-row check that tells you whether to rip the first row before you start.
How this calculator works
The last row is the thing that ruins floors
Divide the room width by the plank width and you almost never get a whole number. Whatever is left over is the width of your final row, jammed against the far wall where everyone looks. If that remainder comes out under about 50 mm you have a problem: a sliver that narrow is fragile, hard to click in, and looks like a mistake.
The fix is decided before the first plank goes down. You rip the first row narrower so the first and last rows come out roughly equal, and the floor reads as deliberate. This calculator works out the last-row width for your room and plank size, accounting for the expansion gap at both walls, and tells you what to cut the first row to if the remainder is too small.
Expansion gap comes off the area, not the order
Every floating floor needs a gap around the perimeter — normally 10 mm — so the boards can move with humidity. The gap shrinks the covered area slightly, but it does not reduce what you buy: the planks at the edge are still cut from full planks, and the offcut is scrap. The calculator uses the full room area for ordering and the gap only for the row geometry.
Packs, not square metres
Flooring is sold in sealed packs and merchants will not split one. After applying the waste allowance the calculator rounds up to whole packs and tells you how much floor you will have left over — which is your repair stock. Keep at least two full planks; one deep scratch from a dropped tool is very common and a matching plank saves the whole floor.
Let it acclimatise. Most manufacturers require the packs to sit flat in the room, unopened, for 48 hours before fitting, so the boards reach the room's humidity. Fitting straight off the van is the most common cause of a floor that peaks or gaps a month later, and it voids most warranties.
Waste allowances used
| Layout | Waste | Why |
|---|---|---|
| Straight, planks along the long wall | 8% | Offcut from the end of each row starts the next row, so very little is scrapped. |
| Straight, planks across the room | 10% | More rows, more end cuts, shorter usable offcuts. |
| Diagonal 45° | 15% | Every plank meets the wall at an angle; both ends are scrap. |
| Herringbone or chevron | 20% | Perimeter is a continuous run of compound cuts, and the pattern cannot absorb offcuts. |
Common questions
Which direction should the planks run?
Along the longest wall is the usual answer: it means fewer rows, fewer end cuts and less waste, and it makes the room read longer. The stronger rule is to run planks along the main light source — parallel to the window wall — because the joints then cast far less shadow. On a suspended timber subfloor, planks must also run across the joists, and that requirement wins over both.
How much stagger do I need between rows?
At least 300 mm between the end joints of adjacent rows, and more for long planks — some manufacturers specify a third of the plank length. Anything less looks like a repeating staircase pattern and is structurally weaker at the joint. Cut the start of each row from the offcut of the previous one and the stagger takes care of itself, which is also where the 8% waste figure comes from.
Do I need underlay if the planks have it attached?
No, and doubling up is a real mistake — too much compression under the click joint causes the tongues to flex and eventually fail. Pre-attached backing normally replaces the foam layer but not a damp-proof membrane, so on a concrete subfloor you may still need a separate DPM sheet underneath.
Can I fit over existing tiles?
Usually yes for a floating floor, provided the tiles are sound, well bonded and flat to within about 3 mm over 2 m. Check for rocking tiles first and lift any that move. The bigger question is height: you are adding 10–20 mm, and door bottoms, thresholds and appliance clearances under a kitchen worktop all need checking before you start.
Why does the calculator ask for room length and width separately?
Because area alone cannot tell you the last-row width, and that is the calculation that changes how you fit the floor rather than how much you buy. The width across the planks sets the row count; the length along them sets how well offcuts feed the next row.
Related
- Waste factor reference table
- Tile calculator — for hard flooring in bathrooms and kitchens
Method last reviewed 2026-09-18. Estimates for planning; follow your manufacturer's fitting instructions, which override anything here.