A 14 by 12 foot room with 8 foot walls, papered in US double rolls (20.5 inches by 33 feet) with an 18 inch straight repeat, needs 12 double rolls. Each strip is cut 9 feet long so the pattern lines up, three strips come out of each roll, and the room takes 36 strips once the door and windows and 10% spare are counted.
How the wallpaper calculator works
Wallpaper is hung in vertical strips, so square footage alone gives the wrong answer. The calculator counts strips instead:
- Cut length: wall height plus a trim allowance, rounded up to a whole number of pattern repeats so every strip starts at the same point in the design. A half-drop match adds half a repeat on average.
- Strips per roll: roll length divided by the cut length, whole strips only. The offcut at the end is too short to hang.
- Strips per wall: wall width divided by the roll width, rounded up, wall by wall.
- Rolls: strips (less the openings, plus waste) divided by strips per roll, rounded up.
Rolls = ⌈ strips × (1 + waste) ÷ ⌊ roll length ÷ cut length ⌋ ⌉
Worked example: a 14 × 12 ft room
| Step | Numbers | Result |
|---|---|---|
| Cut length | 96 in + 4 in trim = 100 in, rounded up to 6 × 18 in | 108 in (9 ft) |
| Strips per roll | 396 in ÷ 108 in | 3 strips |
| Strips around the room | 9 + 8 + 9 + 8 (14 ft ÷ 20.5 in = 8.2, 12 ft ÷ 20.5 in = 7.02) | 34 strips |
| Door and 2 windows | 1 full strip × 84 ÷ 96 + 2 × 1 strip × 48 ÷ 96 | − 1.88 strips |
| With 10% spare | 32.13 × 1.1, rounded up | 36 strips |
| Rolls | 36 ÷ 3 | 12 double rolls |
A door 3 feet wide covers one full 20.5 inch strip, but only for 7 of the 8 feet; the piece above it still comes from a roll. That is why openings save a fraction of a strip, not their whole area. Turn off "Subtract doors and windows" if you prefer the installer's rule of measuring every wall as if it were solid.
Wallpaper roll sizes
| Roll | Width × length | Paper per roll |
|---|---|---|
| US double roll | 20.5 in × 33 ft | 56 sq ft |
| Wide double roll | 27 in × 27 ft (9 yd) | 61 sq ft |
| European roll | 53 cm × 10 m | 5.3 m² (57 sq ft) |
The 20.5 inch by 33 foot double roll and its 56 square feet are the US standard, per InteriorDecorating.com and Graham & Brown's US listings; ROMAN's calculator assumes 21 inches by 33 feet. Farrow & Ball sells rolls 10 meters long and 53 centimeters wide, the European standard width. Wallpaper is often priced per single roll but sold in double rolls, so check which one the price refers to. If your roll is different, choose "Other" and type the width and length from the label; the length is shown in yards too.
InteriorDecorating.com notes that a roll of about 56 square feet hangs only 40 to 50 usable square feet, less with a large repeat. In the example each roll puts three 20.5 inch by 8 foot strips on the wall: 41 square feet.
Wallpaper calculator with pattern repeat
The pattern repeat is the vertical distance before the design repeats itself, printed on the label. ROMAN, the wallcovering adhesive maker, sorts patterns into three matches:
- Random match: no match point, the least waste. Strips are cut to height plus trim.
- Straight match: the design lines up straight across, so every strip starts at the same point. The cut length rounds up to whole repeats.
- Half-drop match: every other strip starts half a repeat lower. ROMAN calls it the match with the most wastage.
On a single 12 by 8 foot wall with a 21 inch half-drop repeat, the cut length is 105 inches plus half a repeat, 115.5 inches (9 feet 7½ inches). Three strips still fit in a 33 foot roll, and the wall's 8 strips plus 10% spare need 3 double rolls.
Wallpaper for one wall or a ceiling
One wall: choose "One wall" and enter its width and height. An accent wall is the most common wallpaper project and the one where a big repeat hurts most, because the leftover end of each roll is rarely usable.
Ceiling: strips run across the shorter side of the room, laid side by side along the longer one. A 14 by 12 foot ceiling with an 18 inch straight repeat has 12 foot 4 inch drops that round up to 13 feet 6 inches; only two fit in a double roll, so the 10 strips need 5 rolls.
Trim allowance and spare rolls
ROMAN advises leaving a few extra inches at the top and bottom of each strip for trimming; the default is 2 inches at each end. Buy all rolls from one batch (the run or dye lot number on the label), since colors can shift between batches, and keep a spare roll for repairs.
Next steps
- Painting the other walls? The paint calculator does the rest of the room, and primes it too.
- Paper above a paneled lower wall: the wainscoting calculator finds the height, and the board and batten calculator spaces battens evenly.
- Need the room's floor area? Use the room square footage calculator.
- New walls first? The drywall calculator counts sheets.
More wall tools are collected in drywall, paint and walls.