Wallpaper Calculator
Result
Rolls to buy
- Strips to cut
- 24
- Strips per roll
- 4
- Surface area in square feet
- 320 ft²
- Surface area in square metres
- 29.73 m²
Wallpaper calculator: enter the total length of the walls, the ceiling height, the size of the roll you are buying and the pattern repeat, and it returns how many strips to cut, how many strips a roll will yield and how many rolls to buy. The arithmetic here is not the area arithmetic the paint and drywall pages use, and two of its consequences surprise people. A strip of wallpaper runs from the ceiling to the floor in one piece, so what decides the order is how many strips the room needs and how many whole strips come off a roll — not how many square feet of wall there are. That is why the doors and windows are not deducted: a strip that crosses a window is still cut full length, and the section over the glass is waste whether you count it or not. And it is why there is no wastage percentage on this page. When a pattern has to be matched, every strip is cut one full repeat longer than the wall is high, because the top of the strip has to land in the same place in the pattern as the strip beside it, and the amount that costs you is already in the repeat field. The roll is the other half of the arithmetic. A roll is sold as a matched pair of numbers — a width and a length — and how many strips come out of it is rounded down, because a strip that does not fit does not fit. A ceiling that is high, or a repeat that is large, can leave a roll unable to yield even one strip, which is a real situation and not a mistake in the numbers.
What one roll covers, and how many strips it yields
| Roll | Coverage per roll (ft²) | Coverage per roll (m²) | Strips per roll at 2.4 m |
|---|---|---|---|
| US double roll (20.5 in × 33 ft) | 56.37 | 5.24 | 4 |
| US single roll (20.5 in × 16.5 ft) | 28.19 | 2.62 | 2 |
| Metric roll (0.53 m × 10 m) | 57.05 | 5.3 | 4 |
| Wide metric roll (1.06 m × 10 m) | 114.1 | 10.6 | 4 |
The first two columns are the raw area of the roll, which is a check figure rather than an answer — the strips are what you buy. The fourth column is the useful one: it is how many whole strips come off a roll against a 2.4 metre ceiling with no pattern to match, and it is rounded down, because a strip that does not fit is not a strip. Every one of those numbers falls as soon as there is a repeat, and it falls further on a higher ceiling: a 33 foot double roll gives four strips at 8 feet, three at 9 feet with a 12 inch repeat, and two at 12 feet. Roll sizes are nominal — check the label on the pattern you are buying, because the width is what the strip count divides by.
Formula
Rolls = ceil( ceil( length ÷ roll width ) ÷ floor( roll length ÷ ( height + pattern repeat ) ) )
- L
- Total length of the walls being papered, in feet
- H
- Ceiling height, in feet — the length of one strip
- u
- Width of the roll, in inches
- r
- Length of one roll, in feet
- p
- Pattern repeat — the distance after which the pattern lines up again, in inches; 0 for a plain or free-match paper
Use it once you have the roll in front of you, because the width, the length and the repeat are all printed on the label and all three change the answer. The repeat is the one people miss: it is written on the roll band, it is a different number for every pattern, and it can be anything from 0 for a plain paper to 24 inches for a large floral. Measure the perimeter of the room rather than one wall, and deduct nothing for the windows and doors — add nothing either, because a room with a lot of openings does not need more strips than its perimeter calls for, only more waste. Measure the ceiling height at the highest point of the room, because a strip has to reach the floor everywhere, and add a little for trimming top and bottom: two inches at each end is the usual allowance and it is not in the arithmetic here. If the room is an awkward shape, treat each wall as its own run and note that the strips are cut to fit one wall each, so a short wall at the end of a run can use a cut-off that a long wall cannot.
Worked examples
A 40 foot run of wall, 8 foot ceiling, a double roll, no repeat
- Strips: the roll is 20.5 inches = 1.7083 feet wide, and 40 ÷ 1.7083 = 23.41, rounded up to 24 strips
- Strip length: 8 feet, because there is no pattern to match
- Strips per roll: 33 ÷ 8 = 4.125, rounded down to 4 whole strips
- Rolls: 24 ÷ 4 = 6 rolls
- Wall area, for checking against a quote: 40 × 8 = 320 square feet (29.73 m²)
These are the page defaults. The important thing to notice is that the area is reported but not used: 320 square feet is a check against the decorator's quote, and the six rolls come from the strips. The rounded-down third step is what makes the difference — a double roll is 33 feet long and a strip is 8 feet, and the fifth strip would need 40 feet, so the 1.125 feet left over is not a strip and never becomes one.
The same wall with a 12 inch pattern repeat
- Strips: 24, unchanged — the pattern does not change how many strips the room needs
- Strip length: 8 feet of wall plus a 12 inch repeat = 9 feet per strip
- Strips per roll: 33 ÷ 9 = 3.667, rounded down to 3 whole strips
- Rolls: 24 ÷ 3 = 8 rolls
Nothing about the room changed and the order went from six rolls to eight. That is the cost of a pattern, and it is why the repeat belongs on the page as a field rather than as a wastage percentage: 12 inches on an 8 foot wall is a 12.5% increase in the length of every strip, which is a third more rolls, and no flat percentage would have got that right for a different ceiling height. A large repeat on a low ceiling costs proportionally more, and a 24 inch repeat on this wall would take 10 rolls.
A 56 foot run, 9 foot ceiling, a 0.53 by 10 metre roll
- The roll is 0.53 metres = 1.7388 feet wide, and 56 ÷ 1.7388 = 32.2, rounded up to 33 strips
- Strip length: 9 feet, no pattern to match
- Strips per roll: the roll is 10 metres = 32.81 feet, and 32.81 ÷ 9 = 3.645, rounded down to 3 strips
- Rolls: 33 ÷ 3 = 11 rolls
- Wall area, for checking against a quote: 56 × 9 = 504 square feet (46.82 m²)
The metric roll is the standard one in China and most of Europe, and against the American double roll it is within two percent in both directions — 0.53 metres against 20.5 inches (0.52 metres) across, 10 metres against 33 feet along — so on this wall the two land on the same answer: 33 strips and three to a roll either way. Roll size earns its place as a field where the widths genuinely differ. The 1.06 metre wide roll is the same length and twice the width, so the same 56 foot run takes 17 strips and six rolls rather than eleven — the roll size is not a detail, it is one of the four numbers in the answer.
Limitations
The strip count and the strips per roll are exact for the roll and the room you describe; what is not exact is everything about the wall itself. Ceiling height is measured at its highest point and a strip is cut full length, so a room with a sloping ceiling or a beam wastes more than this page shows, and the two inches of trim at the top and the bottom of every strip are not in the arithmetic. The pattern repeat is applied as one full repeat per strip, which is the standard allowance and not a guarantee: a pattern that has to be centred on a wall, or one that has to match across a corner, can need more, and a drop-matched or half-drop pattern sometimes needs less. Doors and windows are not deducted, deliberately, because a strip is cut full length whether or not it crosses an opening — but a very large opening does mean more of each strip is waste, so the area shown here overstates how much wall is actually papered. Nothing else in the job is counted: the adhesive and the primer or lining paper under it, the seam roller and the smoothing brush, the filler for the wall, and the trim or border. Two practical notes that this page cannot help with. Walls have to be sized or primed before paper goes on, and a wall that has been painted with a silk or washable finish needs a lining paper rather than extra adhesive. And buy the whole order at once from one batch, because wallpaper is printed in runs and a roll from a different run can be visibly different on the same wall.
Frequently asked questions
- How many rolls of wallpaper do I need for a 12 by 15 foot room?
- About six double rolls, plus one spare. A 12 by 15 room has a 54 foot perimeter; a 20.5 inch wide double roll gives 32 strips, an 8 foot ceiling means four strips come off each roll, and 32 ÷ 4 = 8 rolls — but this page's default is a 40 foot run rather than a full room, and a room where one wall is glass is closer to that. The perimeter and the ceiling height are the two numbers to measure; everything else comes off the label.
- Should I deduct the windows and doors?
- No, and this is the one place on this site where a calculator deliberately does not deduct an opening. Wallpaper is hung in full-height strips: a strip that crosses a window is cut to the ceiling and the floor like every other one, and the section over the glass goes in the bin. So the window does not save a strip, it only makes one strip more wasteful. Deducting it would under-order, which is the one mistake you cannot fix on the second day, because the second roll may come from a different print run.
- What is a pattern repeat and where do I find it?
- The repeat is the distance after which the pattern lines up with itself, and it is printed on the roll band or on the label, usually as a number of inches or centimetres and sometimes with the words straight match, half drop or free match. Straight match means adjacent strips line up at the same height, which is what this page assumes and what the one-repeat allowance is for. Free match, or a plain paper, is a repeat of 0. On a 12 inch repeat and an 8 foot ceiling, the allowance turns 6 rolls into 8 — it is the most expensive field on the page.
- Why is there no wastage percentage on this page?
- Because the thing you are buying is not an area. Rolls are counted from strips, and the two ways you lose paper are already handled: the pattern repeat is a field that lengthens every strip, and the strips-per-roll step rounds down, which covers the short end left on the roll. Adding a percentage on top would count the same loss twice and would not be right for any particular room. Order one extra roll instead — a spare roll kept in the wrapper covers a patch, a mistake and a future repair.
- What does the calculator do if the roll is too short?
- It tells you rather than returning a number, because there is no sensible answer. A roll that is 33 feet long yields four 8 foot strips, but the same roll against a 9 foot ceiling and a 12 inch repeat needs strips of 10 feet and yields only three. A roll shorter than one strip — a 33 foot roll and a 36 foot ceiling, for instance — yields nothing at all, and a strip that does not reach the floor is not a product. In that case you need a longer roll, or you need to paper up to a dado rail and paint below it.
- Which roll size should I buy?
- Whichever the pattern you want is printed on, because the roll size is not a free choice — a given design comes in one width and one length. In North America that is usually a double roll of 20.5 inches by 33 feet, with single rolls of the same width at half the length; in China and much of Europe it is 0.53 by 10 metres, with a wider 1.06 by 10 metre roll for large patterns. The table above compares all four, and the difference is real: the 56 foot wall in the example takes 11 rolls of the 0.53 metre roll and six of the wide 1.06 metre roll.
References
- Approximate Conversions from U.S. Customary Measures to Metric — the chart behind inches, feet, metres and square metres on this page — National Institute of Standards and Technology
- The International System of Units (SI) brochure — the metre the roll widths and lengths are converted to — Bureau International des Poids et Mesures (BIPM)