Wallpaper is hung in vertical strips, and each strip has to be cut from a roll with a fixed length. That is why buying by the square foot gets you into trouble: a roll that holds 56 square feet may produce only four usable strips for an 8-foot wall, with a sliver wasted on each. This wallpaper calculator works from strips, the way a paperhanger thinks, so that the count of rolls is realistic.
How to use the wallpaper calculator
- Enter the total width of the walls you are covering — the perimeter of the room, or just the walls you will paper.
- Enter the wall height from the floor (or the wainscoting) to the ceiling.
- Enter the roll width and length from the label.
- Add the pattern repeat if the paper has a pattern to match, then the area of doors and windows and a spare percentage.
Wallpaper formula
Strips per roll = ⌊ roll length ÷ drop ⌋
Strips needed = ⌈ (perimeter × height − openings) ÷ (roll width × height) ⌉
Rolls = ⌈ strips × (1 + extra) ÷ strips per roll ⌉
The calculation rounds down the number of strips per roll, because leftover paper that is shorter than a wall cannot be used. The pattern repeat is added to each drop, since the paper has to be cut with extra length at the top to match the design.
Worked example: a 12 × 10 ft room, 8 ft ceiling
- Perimeter: 2 × (12 + 10) = 44 ft.
- Roll: 20.5 in × 33 ft. Strips per roll: 396 in ÷ 96 in = 4.125 → 4.
- Strips needed: 44 ft ÷ 1.708 ft = 25.8 → 26.
- Rolls: 26 ÷ 4 = 6.5 → 7 rolls.
If the paper has a 24 in pattern repeat, the drop grows to 120 in and a roll gives only 3 strips, raising the same room to 9 rolls.
Rolls for common rooms (8 ft ceilings, 20.5 in × 33 ft rolls, plain paper)
| Room | Perimeter (ft) | Strips | Rolls |
|---|---|---|---|
| 8 × 10 ft | 36 | 22 | 6 |
| 10 × 10 ft | 40 | 24 | 6 |
| 10 × 12 ft | 44 | 26 | 7 |
| 12 × 12 ft | 48 | 29 | 8 |
| 12 × 15 ft | 54 | 32 | 8 |
| 14 × 16 ft | 60 | 36 | 9 |
Wallpaper buying tips
- Check the batch number. Buy all rolls from the same batch so that the colour matches.
- Roll definitions vary. A “single roll” in some countries is half the length of a “double roll” in others. Always compare dimensions and not the word.
- Match types. A straight-match pattern repeats across the strip, a half-drop pattern offsets alternating strips by half the repeat, which wastes more.
- Accent wall. Enter only the width of that one wall as the perimeter.
Prepare before hanging
Smooth, primed walls help adhesion. Fill holes, sand, remove loose paint and wipe off dust. Start from a plumb line, not from the corner, because few walls are truly straight. After papering, a quick damp sponge wipe removes excess paste.
If you plan to paint instead, use the Paint Calculator. For measuring walls see the Square Footage Calculator, for panel treatments use the Wainscoting Layout Calculator, and for sheet products the Drywall Calculator.
Frequently asked questions
How many rolls of wallpaper do I need for a 12 × 10 room?
With 8 ft ceilings, 20.5-inch wide 33 ft rolls and no pattern repeat, a 12 × 10 ft room (44 ft around) needs 26 strips and 7 rolls, because each roll yields only 4 full-height strips.
What is a pattern repeat?
The vertical distance after which the design repeats. Neighbouring strips must be slid up or down to line up the pattern, which wastes paper at the top or bottom. The repeat is listed on the roll label.
Should I subtract doors and windows?
Only a little. You still need full-height strips above and below openings, so large openings only reduce the strip count somewhat. The calculator subtracts their area, but it never gives fewer strips than the walls actually need.
How much extra should I buy?
Buy an extra roll or 10% for mistakes and later repairs. Wallpaper dye lots differ, so a roll bought later may not match exactly.
How wide is a roll of wallpaper?
In the US, 20.5 inches is a common width. European rolls are often 21 inches (53 cm); wide commercial vinyl is 27 inches or more. Enter your roll’s width and length.