Wallpaper calculator

How wallpaper rolls are calculated

Paperhangers don't buy wallpaper by the square foot. They count drops: full-height strips cut from the roll, hung side by side. The leftover end of each roll is usually too short for another drop, so the count goes like this:

The 4" trim allowance is the extra you cut off at the ceiling and the baseboard, so a slightly out-of-level ceiling or floor doesn't leave a gap. With a random-match paper (repeat 0) there is no rounding. With a pattern repeat, each drop has to start at the same point in the pattern, so its length goes up to the next whole repeat.

Worked example: 48 ft of wall, 8 ft high

The calculator opens on 48 ft of wall, 8 ft high, with 1 door and 2 windows, using metric rolls 20-1/2" wide and 33 ft long and a random-match paper.

1. Drops around the room: 48 ft = 576 in, and 576 ÷ 20.5 = 28.1, rounded up to 29.
2. Openings: 1 × 1 + 2 × ½ = 2 drops, so 29 − 2 = 27 drops to hang.
3. Drop length: 96 in + 4 in = 100 in (8' 4").
4. Drops per roll: 33 ft = 396 in, and 396 ÷ 100 = 3.96, rounded down to 3. Each roll leaves 8' of offcut.
5. Rolls: 27 ÷ 3 = 9 rolls. If these are US double rolls priced per single roll, that is 18 single rolls.

By square feet alone, 384 ft² of wall ÷ 56.4 ft² per roll suggests 7 rolls, even before taking out the openings. That comes up 2 rolls short because it counts the 8' offcuts as usable paper.

Add a pattern repeat of 18" to the same room and each drop becomes 100 ÷ 18 = 5.56, rounded up to 6 repeats = 108 in (9'). A 33 ft roll still gives 3 drops, so the order stays at 9 rolls, but the offcut shrinks to 6'.

Measuring the room

• Measure every wall you plan to paper at about waist height and add them up. Include the wall widths over doors and windows; the openings are taken off separately.
• For a second room, or a stairwell or wall section at a different height, use “+ Add another room”. Each room is counted in whole drops of its own, and rooms with the same drop length share rolls, so the order is rounded once for the whole job.
• Measure the height from the top of the baseboard to the ceiling (or to the crown or chair rail if that is where the paper stops). If the height varies, use the tallest point.
• Read the roll label for the width, the length and the pattern repeat. For US paper sold as double rolls, enter the full double-roll length (for example 27 ft or 33 ft): the drops come off one continuous bolt.
• Using 27" × 27 ft American rolls in the default room instead gives 20 drops at 3 per roll: 7 double rolls. Wider paper means fewer drops, so always calculate with the roll you are actually buying.

Pattern repeat, waste and spare rolls

The repeat is the vertical distance before the pattern starts again; it is printed on the label, often with a match symbol. A large repeat can add most of a repeat's length to every drop. At 18" and up, plan on one extra roll from the same dye lot, because you will lose more paper lining up the first drop on each wall and around openings than the count can predict.

If the calculator shows only one drop per roll, the wall is tall for the roll length. A longer roll, or a different layout planned with your installer, will waste less paper.

Before you open anything, check that every roll has the same dye lot (batch) number. Keep one unopened roll for repairs and return the other unopened extras.