How much lining paper or wallpaper do I need for a room?
Wallpaper is counted in drops, not square metres — which is why a roll goes shorter than the area suggests. Lining paper is counted in square metres plus a bit over ten percent for trimming.
Short answer: wallpaper must be counted in drops, not square metres: divide the room's perimeter by the roll's width (typically 0.53 m) to get the number of drops, then see how many whole drops can be cut from one 10.05 m roll. A room measuring 4.20 × 3.60 m with a 2.50 m ceiling needs 28 drops, which is 10 rolls. Lining paper, on the other hand, is counted in square metres: net wall area plus 10-15% — 34 m² of wall becomes about 39 m², so two rolls of 25 m² each.
Wallpaper: why the area gives you the wrong number
A standard European wallpaper roll measures 0.53 m wide and 10.05 m long = 5.3 m². If you have 34 m² of wall, the sum looks simple: 34 ÷ 5.3 = 6.4 rolls. That number is wrong, and not by a small margin.
The reason is that wallpaper cannot be laid like a jigsaw puzzle. It is hung in whole drops, floor to ceiling. With a 2.50 m ceiling height plus 5 cm of trim at each end, every drop becomes 2.60 m. From a 10.05 m roll you can cut 10.05 ÷ 2.60 = 3.86 drops — so 3 whole drops. The remaining 2.25 m is offcut.
One roll therefore covers 3 × 0.53 = 1.59 m of wall width. Multiplied by the 2.50 m that actually sits on the wall, that is 3.98 m² of covered surface out of a 5.3 m² roll. You lose 25% of every single roll — 2.25 m at the end plus 5 cm at each end of the three drops. That is the quarter the area calculation cannot see.
The calculation in drops
The room is 4.20 × 3.60 m. Perimeter: (4.20 + 3.60) × 2 = 15.60 m. Subtract the door width: 15.60 − 0.90 = 14.70 m.
Number of drops: 14.70 ÷ 0.53 = 27.7 → 28 drops. Windows are not subtracted: paper still has to hang above and below them, cut from a whole drop.
Number of rolls: 28 ÷ 3 drops per roll = 9.3 → 10 rolls.
Ten rolls is 53 m² of wallpaper for 34 m² of net wall. That sounds excessive, but that is how the trade works: the offcut is built into the method, not a sign of sloppiness. You can save yourself a roll or two by using the 2.25 m offcuts for the short pieces above the door and above and below the windows — but plan that in advance, or it ends up in the bin.
A pattern costs extra drops
If the wallpaper has a pattern that must line up drop to drop, more goes to waste. The roll states the repeat — the pattern's recurrence in centimetres — and whether it is a straight match or offset by half. The rule is that the drop length must be rounded up to a whole number of repeats, or the pattern won't line up at the next drop.
Work it out in two steps: 1) round the drop length up to the nearest whole number of repeats. 2) divide the roll's 10.05 m by the new drop length and round down to a whole number — that is drops per roll.
Try it on the example with a 64 cm repeat: the 2.60 m drop must go up to 5 repeats = 3.20 m. 10.05 ÷ 3.20 = 3.1 → still 3 drops per roll, but now with no slack. So take instead an old flat with a 3.20 m ceiling height: the drop becomes 3.30 m, and without a pattern that gives 10.05 ÷ 3.30 = 3.0 → 3 drops. With the 64 cm repeat, the drop must go up to 6 repeats = 3.84 m, and then 10.05 ÷ 3.84 = 2.6 → only 2 drops per roll. That is the jump that suddenly makes the same room cost one and a half times as much. The rule of thumb, if you can't be bothered to calculate: add 5-10% for a free match, 10-20% for a repeat up to around 30 cm, and 20-30% for a large or half-offset repeat.
Always buy all rolls from the same batch — the batch number is printed on the wrapper. Two batches of the same wallpaper can differ visibly in colour, and the difference only shows once the drops are hanging side by side.
Lining paper and glass fabric: where the square metres hold up
Glass fibre paper, glass fabric and paintable non-woven lining behave the opposite way to wallpaper. There is no pattern to match, and the material can be cut and used up, so the sum is pure area.
Net wall area — the wall area minus doors and windows — is the starting point. For the room measuring 4.20 × 3.60 m with a 2.50 m ceiling: perimeter 15.60 m × 2.50 m = 39.0 m² gross, minus 5.0 m² of door and windows = 34.0 m². Add 10-15% for trimming at corners, around frames and at the ceiling and floor edge: 34.0 × 1.13 ≈ 38.4 m².
Lining paper and glass fabric are typically sold in rolls of 1.00 m × 25 m = 25 m², but longer rolls and other widths exist too — check the roll before you calculate. With 25 m² rolls you need two rolls, leaving a good 11 m² spare (50 − 38.4).
Don't forget the adhesive
Lining paper is hung with adhesive rolled onto the wall — not onto the paper. Coverage is printed on the tub and is typically around 4-6 m² per litre; the tub's own instructions always take precedence over a figure from an article. For 34 m² of wall, 5 m² per litre gives 34 ÷ 5 = 6.8 ≈ 7 litres of adhesive, so a 10-litre tub.
An absorbent surface drinks more adhesive. If the wall is freshly filled or bare plasterboard, prime it first — otherwise the wall pulls the adhesive in, the paper lifts at the edges, and you have to re-glue.
And the paint on top
Lining paper and glass fabric are rougher and have more surface than a smooth wall. Allow 10-20% more paint than a smooth wall would need, and expect the first coat after hanging to soak up the most. For the 34.0 m² in the example: two coats = 68 m², plus 15% = 78 m². With a coverage of 6-8 m² per litre per coat, that gives 10-13 litres — against 9-12 litres on a smooth wall.
What the three routes cost relative to each other
The three solutions do not sit in the same price bracket, but the difference is less dramatic than people think — and it mostly comes down to what you choose off the shelf, not the method.
Paint alone on a smooth wall is the cheapest route for a room this size. Lining paper and paint typically costs roughly double, because two rolls of lining paper and a tub of adhesive add on top of the paint. Wallpaper is the only one of the three where the price can run away from you entirely: the gap between the cheapest standard wallpaper and a designer wallpaper is a factor of ten per roll, and you need ten rolls — so the same room can cost anywhere from about the same as lining paper to many times more. The price of wallpaper is a choice you make in the shop, not a figure you can look up.
And the thing that matters most when you choose: lining paper is used because it hides cracks and gives an even surface on old, uneven walls. Choose it for that, not for the price.
The perimeter is the number everything hangs on
Both wallpaper and lining paper stand or fall on one measurement: the room's perimeter. Count a niche, a chimney breast or a bay window wrong, and the error carries straight through to the number of rolls — and with wallpaper, one drop too few can mean an extra roll bought from a different batch in a different colour.
So work out the perimeter twice, and measure it all the way round along the wall, not as length plus width of a rectangle, if the room isn't rectangular. A bay window that is 1.20 m wide and 0.50 m deep adds 0.50 + 1.20 + 0.50 = 2.20 m to the perimeter, where it only removes the 1.20 m it covers — that is a metre more wall than the floor plan suggests.
HouseSense works out the perimeter and wall area from the home's own geometry, scanned with the iPhone's LiDAR or drawn on graph paper in the app, and subtracts doors and windows per room. A long press on a wall folds out the elevation — the wall seen from the front with its openings and measurements — so you can count drops on that single wall before you buy.