How many rolls of wallpaper do I need?

How the wallpaper calculator works

Most wallpaper guides start with the wall area, and that is where they go wrong. A roll is not an area: it is a fixed width — the drop — and a fixed length, and what you hang are whole drops. So the calculator counts drops, not square metres. It divides the wall run by the roll width to find how many drops the wall needs, then divides the roll length by the drop height to find how many of those drops come off one roll. The two numbers meet in the order, then round up, because a part drop and a part roll are both bought whole.

The pattern repeat is what eats a roll

Every drop has to carry a full pattern repeat so the design lines up where two drops meet, and that repeat is added to the drop height. A 2.4 m wall with a 260 mm repeat consumes 2.66 m of roll for every drop. A large repeat makes each drop longer without making the wall taller, so fewer drops come off each roll and the order climbs. A free match — a plain paper or an unpatterned textured vinyl — has no repeat, so each drop is only as long as the wall is high, and the same wall then needs fewer rolls. Leave the repeat at zero for those: the maths still holds, because a zero repeat never divides by anything and never inflates the order.

Drops, rolls and rounding

The calculator rounds in two places, and both are deliberate. Drops round up, because the strip at the end of the wall is cut from a whole drop. Rolls round up too, because wallpaper is sold by the whole roll and a part roll is still a roll. An offcut is normal: it is the price of the repeat, and the reason a spare half-roll so often ends up in the loft for a repair ten years later.

Doors, windows and paste

You can deduct doors and windows, and the calculator turns the area you enter into the length of wall it removes. Treat that saving as optimistic, though: an opening that stops short of the ceiling is cut out of a drop you hang anyway, so it often removes no paper at all. Paste is a planning estimate on top. A typical 5 kg pack pastes about five rolls, but paste-the-wall papers, heavy embossed papers and thirsty or newly plastered walls all change that — always check the product data on the pack.

Measure before you buy

Measure the wall run at its widest and the drop from floor to ceiling, then read the roll width, the roll length and the pattern repeat off the label and type those figures in. Buy every roll at once and check the batch numbers match: a later roll from a different batch can be a shade out, and no calculator can fix that.

Worked example: an 8 m wall in 2.4 m drops

An 8 m run with a 2.4 m drop, in 530 mm × 10 m rolls with no pattern repeat to match.

How we got there

1. 8 m ÷ 530 mm = 16 drops — Drops are counted across the wall, not area: an 8 m run takes 16 drops, and a part drop is cut from a whole one.
2. 4 drops per roll — A 10 m roll at a 2.4 m drop yields 4 drops; a fifth would be too short.
3. 16 ÷ 4 = 4 rolls — Four rolls cover the 19.2 m² of wall.
4. Spare: 1.6 m, about 10% — Because drops leave the roll as whole drops, 4 rolls give about 10% spare rather than a tidy fraction of a roll.
5. 1 pack of paste — At roughly 5 rolls to a pack, 4 rolls need 1 × 5 kg pack of paste.

What you need to buy

The order for the worked example above, straight from this calculator's own shopping list.

• Wallpaper, 530 mm × 10 m — 4 rolls (Covers 19.2 m² of wall from 16 drops at 4 per roll (free match — no repeat to line up). Confirm the roll width and length on the label: a different roll size changes the count.)
• Wallpaper paste (5 kg pack) — 1 pack (ESTIMATE for 4 rolls at roughly 5 rolls a pack. Paste-the-wall and paste-the-paper papers use it differently, and a porous wall drinks more — always check the product data.)

Figures for the worked example only. Change the measurements above and the list recalculates.

Waste and over-ordering

Wallpaper comes off the roll in whole drops, so the waste is the top of the last drop of each strip — here about 10%. A large pattern repeat adds a full repeat to every drop and pushes the roll count up sharply; a free-match paper wastes far less. Buy every roll in one batch, so the colour and the batch number match.