Free UK construction calculators Metric and imperial 2026 UK prices
Work out how much flooring to buy for a room. Choose laminate, engineered wood, LVT or carpet, enter the room size and press Calculate to see the packs with the right wastage, or the length of carpet to cut from a 4 m or 5 m roll, plus underlay, scotia or gripper and door bars.
| Wastage | Packs | Flooring Bought |
|---|
The same room with other allowances, so you can see how wastage changes what you buy.
For hard floors you get the number of packs, the area with wastage and the spare left over; for carpet, the best way to cut it from the roll, the length to buy and any seams. Both show the underlay rolls, the scotia or gripper and the door bars, and a table compares other wastage allowances or roll widths. You can copy the list or save it as a PDF.
The area is length × width. A 5 × 3.8 m room is 19 m². Our wall area calculator works the same way for walls if you are decorating too.
Every floor loses some boards to cuts at the walls, around door frames and pipes, and to the odd damaged board. The more angled the cuts, the more waste:
| Laying pattern | Extra to order | Why |
|---|---|---|
| Straight | 10% | Cuts at the ends of rows and along one wall |
| Diagonal (45°) | 15% | Almost every board at the walls is cut at an angle |
| Herringbone | 15% | Short blocks with angled cuts round the whole edge |
UK retailers such as Flooring Hut suggest about 5% for a simple rectangular room and 10% for most installations, rising to 10 to 15% for herringbone. The calculator uses 10% as a safe default and shows the packs at 5, 10, 15 and 20% so you can choose. A spare pack is also handy for repairs later, because the same batch may not be available.
Packs = room area × (1 + wastage) ÷ m² per pack, rounded up
Pack sizes vary between products, typically about 1.5 to 2.5 m², so always use the figure on the pack you are buying. Buy all the packs from the same batch, and mix boards from several packs as you lay them so any colour variation is spread across the floor.
Floating floors need an expansion gap round the edges, usually about 10 mm, so the boards can move with temperature and humidity. Check the maker's instructions for the exact gap.
Carpet comes off the roll in standard widths, usually 4 m or 5 m, and you buy a length. So the question is not the room area but how the room fits the roll:
The calculator tries the carpet both ways round and picks the one that buys less. A 5 × 3.8 m room fits a 4 m roll as one 5.1 m length (20.4 m²), but a 5 m roll laid the other way needs only 3.9 m (19.5 m²), with no seams either way. Wider rooms often save carpet, or a seam, on a 5 m roll.
Underlay evens out small bumps in the subfloor, reduces noise and adds some warmth. Use the type made for your flooring: thin foam or fibre boards for laminate and wood, rubber or PU foam for carpet. Many rolls cover about 15 m², such as 1.37 × 11 m carpet underlay rolls, so the calculator works in 15 m² rolls; check the roll you buy. On a concrete floor, laminate and wood also need a damp proof membrane, which some underlays include. If your LVT already has underlay attached, do not add another layer unless the maker allows it.
The calculator works these out from the perimeter of the room, less about 0.8 m for each doorway.
A 5 × 3.8 m living room with one door: 19 m² of floor and 16.8 m of edge.
| Flooring | What to buy |
|---|---|
| Laminate, 2 m² packs, straight lay | 19 × 1.10 = 20.9 m², so 11 packs (22 m²) |
| Carpet on a 4 m roll | One piece 4 × 5.1 m = 20.4 m² |
| Carpet on a 5 m roll | One piece 5 × 3.9 m = 19.5 m² |
| Underlay | 2 rolls of 15 m² |
| Scotia or gripper | 7 × 2.4 m scotia, or 12 × 1.52 m gripper |
| Door bar | 1 |
For the subfloor, our floor screed calculator works out a new screed, and our heat loss calculator helps if you are fitting underfloor heating.
Multiply the room length by the width to get the area in m², add 10% for cutting, and divide by the m² in a pack, rounding up to whole packs.
About 10% for most rooms, 5% for a simple rectangle, and 15% for diagonal or herringbone layouts.
Carpet is sold by the length off a 4 m or 5 m roll. If the room is narrower than the roll, buy one length of the other side plus about 100 mm; wider rooms need a seam.
Whichever fits the room with the least waste and fewest seams. A room up to 5 m wide fits a 5 m roll in one piece.
The same as the floor area. Rolls often cover about 15 m², so a 19 m² room needs two.
Not if the planks have underlay built in; adding another layer can damage the joints. Check the maker's instructions.
One for each doorway where the flooring stops or meets a different floor.
Usually about 10 mm around the edges of the room, but follow the maker's instructions for your floor.
Wastage guidance from UK flooring retailers including Flooring Hut. Underlay roll and gripper sizes from UK merchant product data. Reviewed November 2026.