How to use the wallpaper calculator
- Add up the widths of all walls you will paper. Do not subtract doors or windows.
- Enter the wall height.
- Enter the roll width and length from the label.
- Enter the pattern repeat, or 0 for plain or random-match paper.
Check the pattern repeat on the roll label before you buy. On Decoratoradvice we find a large repeat wastes more paper per strip than people expect.
Wallpaper formula
Strips needed = total wall width ÷ roll width, rounded up
Strip length = wall height + pattern repeat
Strips per roll = roll length ÷ strip length, rounded down
Rolls = strips needed ÷ strips per roll, rounded up
Wallpaper is hung in full-height strips, so the count is based on strips, not area. Leftover pieces shorter than the wall are rarely usable.
Worked example
Three walls totalling 24 ft, 8 ft high, in 20.5 in × 33 ft rolls with no repeat:
Strips: 288 in ÷ 20.5 in = 14.05, so 15 strips
Strips per roll: 33 ÷ 8 = 4.1, so 4
Rolls: 15 ÷ 4 = 3.75, so 4 rolls
With a 21 in pattern repeat, each strip needs 8 ft + 1.75 ft = 9.75 ft, so a roll gives only 3 strips and you need 5 rolls.
Common roll sizes
| Roll | Width | Length |
|---|---|---|
| Common US double roll | 20.5 in | 33 ft |
| Common European roll | 53 cm | 10.05 m |
Sizes vary by brand. Always use the dimensions on your roll's label.
Tips
- Buy one extra roll from the same batch for repairs and mistakes. Batch numbers can differ in colour.
- Start papering at the least visible corner, where the last strip will meet the first.
- Prime or size the walls if the manufacturer recommends it. If you are choosing between wallpaper and paint for a room, the paint calculator works from the same measurements.
Common mistakes
- Using area instead of strips. Dividing wall area by roll area overestimates how much paper is usable.
- Ignoring the pattern repeat. A large repeat can cut a roll from 4 strips to 3.
- Subtracting doors and windows. The offcuts above and below them seldom match the pattern.
Frequently asked questions
How many rolls of wallpaper do I need for a 12 × 12 room?
The perimeter is 48 ft. With 8 ft walls and 20.5 in × 33 ft rolls: 576 ÷ 20.5 = 28.1, so 29 strips; at 4 strips per roll, 8 rolls.
What is a pattern repeat?
The vertical distance before the pattern repeats. Each strip must be cut long enough to line up the pattern with the next strip.
Should I subtract windows and doors?
Not in the estimate. Offcuts from around openings are usually too short or mismatched to reuse.
What is the difference between a single and double roll?
In the US, wallpaper is often priced per single roll but sold in double rolls. Check the length on the label.
Do I need to prepare the walls?
Walls should be smooth and sound. New drywall from the drywall calculator project usually needs priming first.
How do I finish the bottom edge?
Baseboard covers the cut edge at the floor; the baseboard calculator counts pieces.
Key takeaways
- Count full-height strips, not area.
- Strip length = wall height + pattern repeat.
- Round strips up and strips-per-roll down.
- Buy one extra roll from the same batch.