Wallpaper rolls:
count the strips first, then the rolls

Why the strip count beats a simple area calculation

It is tempting to work out the wall area and divide by the area of a roll. It sometimes works. It fails quietly when a roll cannot be used in full. Paper is hung in vertical strips, and a strip cannot be made from the leftover short piece at the end of a roll, so a roll of 10 m gives a whole number of full-height strips, with the remainder wasted.

Counting strips follows how the job is actually done. First find how many strips span the walls. Then find how many full-height strips one roll provides. Divide, and round up. The two roundings, to a whole strip and to a whole roll, are where the extra paper comes from.

There is a further reason strips are the better unit: the same figures can be used to price the job. Paper is sold by the roll, and the strip count tells a decorator how long the hanging will take, since each strip is cut, pasted, hung and trimmed. A room that needs 34 strips is a half-day job for a competent decorator, whatever its floor area.

The three-step method

Keep the three roundings separate, and do each one at the stage it belongs. Rounding the result of the division in the first step, then again in the third, is what gives a reliable order.

Worked example: an 18 m perimeter, 2.4 m walls

Compare with the area shortcut. The wall area is 18 × 2.4 = 43.2 m², and each roll covers 0.53 × 10 = 5.3 m². Divide and you get 8.15, which rounds to 9. It agrees here, but only by luck: each roll's last 1.7 m is wasted, and that waste simply happens to fit inside the rounding.

Add a trim allowance and the answer shifts. If you allow 10 cm at the top and bottom for trimming, each strip is 2.6 m, 10 ÷ 2.6 gives 3.85, which rounds down to 3 strips per roll, and 34 ÷ 3 gives 11.3, or 12 rolls. Three extra rolls from one extra 20 cm per strip is the kind of change an area calculation never reveals.

Pattern repeat and matching

A plain paper can be hung from any part of the roll. A patterned paper must be matched from one drop to the next, so the start of each strip is positioned to align the design. The distance after which the pattern repeats is printed on the label as the pattern repeat. In the worst case, each strip wastes up to one full repeat.

The repeat is a worst-case figure for planning. A good paper hanger cuts strips in sequence and reuses offcuts, so the final order sometimes needs one roll fewer, although a spare roll is cheaper than a mismatched batch.

Paste-the-wall papers and wider rolls change the numbers. Non-woven paper rolls are often 0.53 m wide while some modern murals and wide-width vinyls are 0.68 m or more. Always run the formula with the measurement on the label of the product you are buying, and not with a width remembered from a previous project.

Measuring the room properly

Accuracy at this stage saves rolls later. Measure each wall at its full width, and take the height at more than one point, since ceilings and floors are rarely level in older buildings. Use the largest height you find.

1. 1Measure the width of each wall to be papered, skipping any alcoves or sections that will not be covered, and add them to give the perimeter.
2. 2Measure the height from the skirting board to the ceiling or picture rail in at least two places and keep the larger figure.
3. 3Add a trim allowance, commonly around 5 to 10 cm in total at each end of a strip, depending on the paper and your confidence with a blade.
4. 4Read the roll width, roll length and pattern repeat from the label, because manufacturers differ.
5. 5Run the three formulas, and check the answer against a rough area estimate as a sanity test.

Stairwells and gables break the pattern: the strips have different lengths, which makes the strip-per-roll step unreliable. In those spaces, measure the longest strip needed, assume that length for every strip, and accept a slightly generous order. Alternatively, sketch each wall and count the strips by hand, reusing the offcut from the long drop for the short drop beside it.

Doors, windows and a spare roll

Openings reduce the paper needed but not as much as their area suggests. The strip above a door or under a window still has to be hung, and each is a short piece cut from a full-length strip. A common practice is to deduct a full strip only for a wide opening, such as a patio door, and otherwise leave the strip count as it is.

• Measure the perimeter along the walls to be papered, not the entire room, if a chimney breast or feature wall will be done differently.
• Add about 1 spare roll for ordering from one batch number, because the colour shade can vary between print runs.
• Keep offcuts; they patch awkward corners and may be useful for repairs later.
• Check the roll width and length on the label, since imported and wide-format papers have other sizes.