Wallpaper Calculator
Rolls depend on strips, strip length and pattern repeat - not just wall area. This calculator does the strip math properly.
How it works
- Perimeter = (length + width) x 2
- Strips needed = perimeter / roll width, rounded UP
- Strip length = wall height plus trim allowance, rounded UP to the next full pattern repeat
- Rolls = strips x strip length / roll length, rounded UP, plus waste
Worked example
A 12 ft x 10 ft room has a 44 ft perimeter. With a 20.5 in wide roll you need 26 strips. At 8 ft walls with a small trim allowance each strip is about 8.3 ft, using 216 ft of paper. Rolls are 33 ft, so 216 / 33 = 6.6 - with a 10% spare allowance, buy 8 rolls, about $320 at $40 a roll. Add a 21 in pattern repeat and strips get longer, which is why bold patterns eat rolls.
Assumptions to know
- A 4 inch (10 cm) trim allowance per strip is included in the strip length.
- Doors and windows are not subtracted - their offcuts cover mistakes and small areas like above doors; this is standard wallpaper practice.
- Double rolls: if your roll is sold as a double roll, enter its full length (usually about 66 ft / 20 m).
Results are planning estimates only. Always check the coverage and instructions on the actual product you buy, and measure your own space carefully before ordering. When in doubt, a little extra material is cheaper than a second trip or a stalled job.
Frequently asked questions
How many rolls of wallpaper do I need for a bedroom?
A typical 12 x 10 ft bedroom with 8 ft walls needs about 5 to 7 standard rolls, depending on pattern repeat. Always check your room with the calculator and buy one extra roll if the pattern is bold.
Why does pattern repeat use so much paper?
Each strip has to start at a point where the pattern lines up with its neighbor, so strips are cut longer than the wall - sometimes almost a full repeat longer. The offcut is waste you cannot avoid.
Should I buy all rolls from the same batch?
Yes. Wallpaper is printed in runs (batch or lot numbers) and color shifts slightly between them. Buy everything at once with the same batch number, and keep the number noted for repairs.
Can I wallpaper over old wallpaper?
It is not recommended. New paste can loosen the old layer and seams show through. Stripping first gives a flatter, longer lasting result.