Wallpaper is worked out in drops — the vertical strips you hang. Count how many drops go around the room, work out how many drops you get from one roll, and divide. The pattern repeat and a waste allowance do the rest. Here is the whole method.
Step 1: drops around the room
Measure the room’s perimeter and divide by the roll width, rounding up. A 13 × 10 ft room is 46 ft (14 m) around; with a 20.5 in (0.53 m) roll that is 46 ÷ 1.71 ≈ 27 drops to cover the walls. Don’t subtract normal doors and windows — you hang the drop across them and cut the paper out afterwards, and the offcut is your spare.
Step 2: drops per roll
Divide the roll length by one drop length — your wall height plus a few inches to trim top and bottom — rounding down. A 9 ft (2.7 m) wall needs a drop of about 9 ft 4 in (2.8 m); a 33 ft (10.05 m) roll gives 33 ÷ 9.3 = 3 drops per roll. So 27 drops ÷ 3 = 9 rolls before waste.
| Roll | Size | Coverage |
|---|---|---|
| Standard (worldwide) | 10.05 m × 53 cm | ~5.3 m² (57 sq ft) |
| US double roll | ~11 yd × 20.5 in | ~56 sq ft (5.2 m²) |
Wallpaper Calculator
Enter your room, roll size and pattern repeat for the drops, drops per roll and rolls to buy.
Pattern repeat — the hidden cost
A plain paper wastes almost nothing: a drop is just the wall height plus trim. A patterned paper is different — every drop has to be cut to a whole number of repeats so the design lines up between strips. If the repeat is 25 in (640 mm), each drop is rounded up to the next multiple of 25 in, and the offcut is wasted. A large repeat can easily cost you an extra roll or two, which is why it is the first thing to enter after the room size.
A straight match lines the pattern up level across every drop. A drop (offset) match shifts alternate strips by half the repeat, staggering the pattern and wasting a little more at the top of every other drop — lean towards the higher end of your waste allowance for those.
How much extra to buy
Add about 10–15%, and never fewer than one spare roll. You lose paper to trimming, matching, mistakes and the odd damaged length — and a repair years later needs paper from the same batch. Buy every roll in one go and check the batch (or run) numbers match, because separate batches can differ slightly in shade. Keep a labelled spare for touch-ups.
Working in metric?
The method is identical — only the units change. Perimeter ÷ roll width for the drops, roll length ÷ drop length for the drops per roll. The standard 10.05 m × 53 cm roll gives the same 9 rolls for the example room. The calculator does both systems — just flip the units switch.