Hardboard Floor Calculator
How much hardboard do you need to level a floor? The area rule is usually close, but it cannot tell you when a room needs a sheet more or less, because the sheets go across the floorboards with staggered joints, and every row ends in a cut. Enter your room and which way the floorboards run, and get the sheets laid out as B&Q's guide says, the offcuts reused, and the nails counted.
Last reviewed: 30 September 2026
Room
Sheets go with their long side across the floorboards (B&Q). Leave the extra allowance at 0%: the plan already counts every cut. Use it for hearths, pipes and door frames the rectangle does not show.
How Much Hardboard Do I Need?
The usual answer is the floor area plus 10%, divided by the sheet area. On big sheets it is right for most rooms, but not all: for a 3.0m × 2.5m room on 2440 × 1220mm sheets it gives 3 sheets, and the room needs 4. In the table below it matches the plan in 4 of 5 rooms on 2440mm sheets and is short in 1. On 1220 × 607mm sheets it is over in 5 of 5.
That is because hardboard is laid to a pattern. B&Q's guide says the long side goes at 90 degrees to the floorboards, starting in the centre of the room, with the joints staggered like a brick wall. Every row ends in a cut piece at both walls, the edge rows are cut narrower, and an offcut is only useful if it fits somewhere else. So this calculator lays every sheet out and reuses offcuts with straight cuts, turning a piece round where that fits.
How the Layout Works
- Long side across the floorboards. B&Q: "so that the long side is at a 90 degree angle to the floorboards".
- Joints staggered like brickwork. B&Q: at least a quarter of a sheet between the joints in neighbouring rows. We offset every other row by half a sheet.
- Set out from the centre. B&Q says to start in the centre. We try shifting the pattern by up to half a sheet to use the fewest sheets with no slivers under 100mm (our rule).
- Offcuts reused. Pieces the same width go end to end, and narrow strips share a sheet side by side, with a 3mm saw cut. A piece can be turned 90 degrees to fit an offcut (our rule).
- Nails counted. A grid on every piece at B&Q's limits: no more than 150mm apart and no more than 15mm from an edge.
What it does not do: L-shaped rooms as one floor, hearths, pipes and door frames. Enter each rectangle as its own room and use the extra allowance for the awkward bits.
Sheet Sizes, With Sources
Every size in the dropdown has a Wickes product page, and no product page means no dropdown entry. All are 3mm, the thickness B&Q's guide says to use.
| Sheet | Product page |
|---|---|
| 2440 × 1220 × 3mm | Wickes General Purpose Hardboard Sheet, 3 x 1220 x 2440mm |
| 1829 × 607 × 3mm | Wickes General Purpose Hardboard Sheet, 3 x 607 x 1829mm |
| 1220 × 607 × 3mm | Wickes General Purpose Hardboard Sheet, 3 x 607 x 1220mm |
The laying rules are from B&Q's guide to levelling a floor. The half-sheet stagger, the 100mm shortest piece and the way offcuts are reused are our own working.
Common Rooms: Sheets Needed
Generated from the calculator above, with the floorboards along the room's length and nothing added. The area rule is the floor area plus 10%, over the sheet area.
| Room | 2440 × 1220 Sheets | Area Rule | 1220 × 607 Sheets | Area Rule | Nails (2440 sheets) |
|---|---|---|---|---|---|
| 3.0m × 2.5m | 4 | 3 (short) | 11 | 12 | 480 |
| 3.5m × 3.0m | 4 | 4 | 15 | 16 | 616 |
| 4.0m × 3.5m | 6 | 6 | 20 | 21 | 810 |
| 4.5m × 3.5m | 6 | 6 | 23 | 24 | 918 |
| 5.0m × 4.0m | 8 | 8 | 29 | 30 | 1188 |
Frequently Asked Questions
How many sheets of hardboard do I need?
The usual sum is the floor area plus 10%, divided by the sheet area. For a 3.0m × 2.5m room on 2440 × 1220mm sheets that is 3 sheets, but laid the way B&Q's guide says it needs 4. The sheets go with their long side across the floorboards, and the joints are staggered like brickwork, so every row ends in a cut piece and the edge rows are cut narrower. This calculator lays every sheet out, reuses the offcuts where they fit, and counts the sheets to buy.
Which way should hardboard go?
B&Q's guide says to start in the centre of the room and lay the boards so the long side is at 90 degrees to the floorboards. Tell the calculator which way your floorboards run and it lays the sheets across them. It sets the pattern out from the middle and tries shifting it by up to half a sheet to use the fewest sheets with no slivers under 100mm at the edges, which is our own rule.
How far apart should the joints be?
B&Q says to stagger the joints like a brick wall, with at least a quarter of a sheet length between the joints in neighbouring rows. The calculator offsets every other row by half a sheet, which is more than that.
How many nails do I need?
B&Q says nails at a maximum spacing of 150mm in any direction and not more than 15mm from the edge, nailing the long side first and working diagonally across in a pyramid pattern. At those limits a full 2440 × 1220mm sheet takes 162 nails and a 1220 × 607mm sheet takes 45. The calculator counts every piece, so a 4.0m × 3.5m room takes about 810.
Do I need to condition hardboard?
Yes. B&Q says to scrub water into the rough side of each sheet, then lay them flat on top of one another in the room for 24 hours before fitting, so they can acclimatise. It does not change how many sheets you need.
Which side of hardboard goes up?
B&Q says smooth side up for self-adhesive or loose-laid floor coverings, and rough side up for coverings that are stuck down with adhesive, and to check the flooring maker's advice.
Which sheet size is best?
Big sheets mean fewer joints and fewer sheets to carry, and small ones fit up a staircase and into a car. The table below gives both for common rooms. Wickes sells 3mm hardboard in 2440 × 1220, 1829 × 607 and 1220 × 607mm, each with a product page listed below.