Wallpaper Calculator
The wallpaper calculator below counts strips to work out how many rolls a room needs, including what the pattern repeat costs you, which an area estimate never shows.
Rolls by Strip Count
The accurate method: how many strips the walls need, and how many strips each roll yields.
Rolls by Area
The quick method. Useful for a rough order, but it does not know where the strips fall or what the repeat costs.
Wallpaper Cost
How to use the Wallpaper Calculator
Measure the room and the wall height floor to ceiling. Then find the pattern repeat on the roll label, it is usually printed alongside the roll dimensions, and it is the number that decides how much you throw away.
Use Rolls for the real answer. It works out how many strips the perimeter needs, how long each strip has to be cut once the repeat is honoured, and how many of those strips a roll actually yields.
Area is there for a rough figure when the paper has not been chosen yet.
Wallpaper formula
strips needed = ceiling(perimeter ÷ roll width)cut length = ceiling((height + trim) ÷ repeat) × repeatstrips per roll = floor(roll length ÷ cut length)rolls = ceiling(strips needed ÷ strips per roll)
For a random-match paper the repeat drops out and the cut length is simply the height plus trim.
A half-drop match is different. Each strip starts half a repeat below the one before it, so cutting in sequence off one bolt the cut length has to advance the pattern by an odd number of half repeats, not by a whole repeat:
cut length = smallest odd multiple of (repeat ÷ 2) that is ≥ height + trim
That is not the same as the straight-match figure, and it is not always larger. On a 100 in drop a 24 in repeat needs 108 in against the straight match’s 120, but a 20 in repeat needs 110 in where a straight match would have cut 100, and cutting to 100 leaves the strip out of phase and the job short.
| Roll | Width | Length | Coverage |
|---|---|---|---|
| European double | 20.5 in | 33 ft | 56.4 sq ft |
| European single | 20.5 in | 16.5 ft | 28.2 sq ft |
| American double | 27 in | 27 ft | 60.8 sq ft |
| American single | 27 in | 13.5 ft | 30.4 sq ft |
| Commercial bolt | 54 in | 30 yd | 405 sq ft |
Worked example
A 14 × 12 ft room with 9 ft walls, one door and two windows, in a 20.5 in × 33 ft double roll with a 21 in straight-match repeat:
- Perimeter: 52 ft, less about 3 ft for the door and 6 ft for the windows = 43 ft usable
- Strips: 43 × 12 ÷ 20.5 = 25.2 → 26 strips
- Cut length: 108 + 4 = 112 in, rounded up to the next 21 in multiple = 126 in
- Strips per roll: 396 ÷ 126 = 3.14 → 3 strips
- Rolls: 26 ÷ 3 = 8.67 → 9 double rolls
The repeat is costing 14 in on every strip. By area the same room looks like seven rolls, or eight with a fifteen percent allowance, either way short of the nine the strips actually need.
What the result means
The repeat is the hidden cost. A wall that is just over a repeat multiple wastes almost a whole repeat on every strip. Where the paper allows it, a slightly shorter drop or a picture rail can pull the cut back under the line.
A roll rarely divides evenly. Three strips out of a 33 ft roll leaves 18 in of usable paper, enough for over-door and over-window pieces, but not for a full drop. That leftover is why the strip method beats the area method.
Openings only help when they are full height. A window in the middle of a wall still needs paper above and below it, and those short pieces usually come off the same roll. Deducting the full window area over-trims the order.
Order it all at once. Wallpaper is printed in batches and the colour drifts between them. The batch number is on the label, check every roll matches before you start.
Common mistakes
- Estimating by square footage. It ignores the repeat and the strip width, and it is usually short.
- Buying single rolls when the price is quoted per single. Wallpaper is nearly always sold as a double roll priced by the single. Check which you are ordering.
- Mixing batch numbers. The colour difference is invisible on the roll and obvious on the wall.
- Forgetting the trim. Two inches top and bottom is not optional, ceilings are not level and baseboards are not straight.
- Not ordering a spare. One extra roll costs far less than finding the batch is discontinued when a strip tears.
Frequently asked questions
How many rolls of wallpaper do I need for a 12 by 14 foot room?
With 9 foot walls, one door, two windows and a standard 20.5 inch by 33 foot double roll with a 21 inch repeat, about nine double rolls. A square-footage estimate puts the same room at seven or eight, which is how jobs end up a roll short.
How do I calculate wallpaper rolls?
Divide the wall perimeter by the roll width to get the number of strips. Work out the cut length by rounding the wall height plus trim up to the next whole pattern repeat. Divide the roll length by that cut length and round down for strips per roll, then divide the strips needed by strips per roll.
What is a pattern repeat and why does it matter?
It is the vertical distance before the design starts again, printed on the roll label. Every strip has to be cut at a whole number of repeats so the pattern lines up with its neighbour, so a 25 inch repeat on a 108 inch wall forces a 125 inch cut and wastes 17 inches per strip.
Should I subtract doors and windows?
Only partly. A full height doorway removes a real strip of wall, but a window in the middle of a wall still needs paper above and below it. Deducting the whole window area is the most common way to end up a roll short.
What is the difference between a single and a double roll?
A double roll is one continuous bolt containing twice the length of a single. Almost all wallpaper ships as double rolls, but the price is often quoted per single roll, which makes it look half what it is. The longer bolt also yields more full strips with less waste.
How much extra wallpaper should I buy?
One spare roll from the same batch. Ten to fifteen percent is the usual allowance on the area method, but the strip method already carries the real waste, so what you want is a whole spare roll rather than a percentage.
Sources and assumptions
Roll dimensions are the standard North American and European trade sizes. Individual papers vary, the width, length and repeat are printed on every roll label and should be used in preference to the presets here.
The strip method is the one paperhangers use. The area method is included for comparison because it is what most online estimates give, and the difference between the two is the point.
Opening deductions here assume a doorway removes roughly 3 ft of usable perimeter and a window roughly 3 ft, which is deliberately conservative, paper is still needed above and below a window.
The half-drop calculation assumes strips are cut in sequence off one bolt, working straight along the wall, which is what allows the half-repeat cut. Cut out of sequence and each strip needs a full repeat instead, allow an extra roll.