Understanding your result
The headline is the rolls to buy, and the sub-line gives the drops, their length and how many each roll yields. The three figures show the drops needed, the drops per roll and the share of the paper that ends up as roll ends.
The table goes step by step: the wall length (the room’s perimeter or your measured run), the length still to cover after the openings, the roll, the drop length with the trim and the repeat, the drops per roll, the drops needed, the rolls, any spare, and for US rolls the count in single rolls. Roll-end waste of 20 to 30% is normal and not all lost: the short pieces above doors and under windows come from those ends.
Rolls are the first number; the others follow from it. The paste calculator takes the roll count for the paste and the wall primer; the wallpaper cost calculator prices the rolls, the paste and the installer; and the paint versus wallpaper calculator compares the whole job with painting the same room. For self-adhesive panels, the peel-and-stick calculator works the same way with panel sizes.
How we calculate this
Doors take out their full width of drops, 3 ft each. Windows take out only half their 3 ft width, because the short pieces above and below a window are cut from roll ends rather than from new drops. The trim allowance is 2 in at the ceiling and 2 in at the baseboard. A straight match rounds each drop up to a whole number of repeats so that every strip starts at the same point; a drop match adds half a repeat on average. The method is the one the wallpaper roll guide works through by hand, and the drop count is the reason two rolls of the same area can hang different amounts of wall.
The roll sizes are the standard ones: US double rolls of 20.5 in × 33 ft (about 56 sq ft) and 27 in × 27 ft (about 61 sq ft), and the European roll of 0.53 × 10.05 m (about 5.3 m², 57 sq ft). Any other size can be entered from the label. They are listed with the other fixed sizes on the standard sizes page.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| US double roll | 20.5 in × 33 ft (56 sq ft) | Common US double-roll size; a US single roll is a 36 sq ft pricing unit |
| US wide double roll | 27 in × 27 ft (61 sq ft) | The other common US size |
| European roll | 0.53 × 10.05 m (5.3 m²) | The standard European roll |
| Trim allowance | 4 in per drop | 2 in top and bottom, standard paperhanging practice |
| Door | 3 ft of drops removed | A standard 36 in door |
| Window | half of 3 ft removed | Pieces above and below come from roll ends |
| Pattern repeat | 21 in, straight match | A common repeat; the label gives the real one |
Assumptions last reviewed October 8, 2026.
The calculator does not model sloped ceilings, dormers or stairwells, where drops vary in length (measure the longest drops separately and add them), papering around a fireplace (enter it as doors), or ceilings. It assumes every drop is cut from a fresh section of roll; skilled hangers sometimes squeeze an extra short drop from the ends.
Two worked examples
A 12 × 10 bedroom, 21 in straight repeat
8 ft walls, one door, two windows, US double rolls of 20.5 in × 33 ft.
- To cover: 44 − 3 − 3 = 38 ft = 456 in; drops: 456 ÷ 20.5 = 22.2, so 23
- Drop: 96 + 4 = 100 in, rounded up to 5 repeats of 21 in = 105 in
- Drops per roll: 396 ÷ 105 = 3.77, so 3
- Rolls: ⌈23 ÷ 3⌉ = 8 double rolls, 16 single rolls; 24% ends up as roll ends
With a 24 in drop-match repeat instead, each drop is 132 in and the roll still gives 3, so it is 8 rolls again, but almost nothing is wasted. On European rolls in metric, the same room is 22 drops of 265 cm and 8 rolls.
One accent wall, and a taller room in wide paper
A 14 ft accent wall with a random-match paper, no openings: 9 drops of 100 in, 3 to a roll, 3 double rolls, and a 4th as a spare from the same batch.
The 12 × 10 room with 9 ft walls in 27 in paper with a 25 in repeat: 17 drops of 125 in, but only 2 per 27 ft roll, so 9 double rolls. The wider paper means fewer drops, but the shorter roll gives fewer of them, which is why the drop count matters more than the area.
Where to find your inputs
Room or run. Length and width for a room; for a single wall or part of a room, the width you are papering.
Height. From the baseboard to the ceiling or the crown; if there is a chair rail and you paper above it, from the rail.
Doors and windows. Count every opening in the walls being papered.
Roll size, repeat and match. On the label or the sample book: the roll width and length, the repeat in inches or centimetres, and the match type (straight, half-drop or random).
Common mistakes
- Dividing the wall area by the roll area. Drops, not square feet, decide the count.
- Ignoring the repeat. A long repeat can add two rolls to a room.
- Pricing double rolls as singles. Check whether the price is per single roll.
- Buying rolls from two batches. Check the batch number; buy the spare at the same time.
- Subtracting whole windows. The pieces above and below need paper too.
- Forgetting the trim allowance. Drops cut exactly to height leave gaps.
Questions people ask
- How many rolls of wallpaper for a 10 × 12 room?
- With 8 ft walls, a door and two windows, there is about 38 ft of wall to cover, which in 20.5 in paper is 23 drops. With a 21 in straight-match repeat each drop is 105 in, three to a 33 ft double roll, so the room takes 8 double rolls, 16 single rolls in US pricing terms.
- What is a drop?
- One full-height strip of paper, cut from the roll to the wall height plus a little at the top and bottom for trimming and enough extra to line the pattern up with the strip beside it. A wall of 14 ft in 20.5 in paper takes 9 drops.
- How does the pattern repeat change the number of rolls?
- Each drop has to start at the same point in the pattern, so its length is rounded up to a whole number of repeats. On an 8 ft wall a 21 in repeat makes each drop 105 in instead of 100, and a 24 in repeat makes it 120. A longer drop can mean one drop fewer per roll, which on a room adds a roll or two.
- What is a drop match?
- A pattern where alternate strips are offset by half a repeat. It wastes about half a repeat more per drop on average, but cutting alternate drops from two rolls recovers much of it. Straight-match patterns line up across the top; random or free-match papers need no allowance at all.
- What is the difference between a single roll and a double roll?
- In the US, a single roll is a pricing unit of about 36 sq ft, but paper is sold in double rolls of 56 to 61 sq ft depending on the width. The calculator counts double rolls and shows the single-roll count, because prices are often per single roll.
- Should I buy a spare roll?
- Yes, one from the same batch, for repairs and mistakes. A roll bought later can come from a different printing and differ slightly in shade. Add it in the spare field.