How it works
The calculator uses the drop method: it works out the length of each strip, how many strips fit on one roll and how many strips the walls need.
Drop = Wall height + Trim (rounded up to whole pattern repeats)
Drops = ⌈ Wall length ÷ Roll width ⌉
Drops per roll = ⌊ Roll length ÷ Drop ⌋
Rolls = ⌈ Drops ÷ Drops per roll ⌉
⌈ ⌉ means rounding up and ⌊ ⌋ rounding down. You need a whole drop to cover each roll-width of wall, and a part-drop at the end of a roll can’t be hung, so it is not counted.
US roll sizes vary by product, so the US roll fields start empty; the metric defaults are Erismann’s 0.53 × 10.05 m roll. Until a roll size is entered, only the wall area is shown.
Worked example
Inputs
- Measure by
- Room length × width
- Room length
- 14 ft
- Room width
- 12 ft
- Wall height
- 8 ft
- Roll width
- 20.5 in
- Roll length
- 33 ft
- Pattern repeat
- 0 in
- Trim allowance per drop
- 0 in
Result
- Wall area
- 416 sq ft
- Drops
- 31
- Drops per roll
- 4
- Rolls
- 8
Common mistakes
- Calculating from wall area alone. Paper is hung in full-height drops, and the leftover at the end of each roll is often too short to use, so area-based estimates come out low.
- Ignoring the pattern repeat. Every drop has to start at the same point in the pattern, so a large repeat can reduce the number of drops per roll.
- Entering the single-roll size when the paper is sold in double rolls – or the other way round. Use the size of the roll you actually buy.
- Buying rolls from different batches. Colors can vary between batch numbers, and a second order may not match.
Assumptions and limits
- The drop method – each drop is the wall height plus trim, rounded up to whole pattern repeats when there is a repeat.
- Doors and windows are deliberately not subtracted. The paper around them still has to be cut from full drops and pattern-matched.
- Drops per roll are rounded down, so a part-drop left at the end of a roll is treated as offcut.
- In room mode, all four walls of a rectangle are papered to the same height. Ceilings are not included.
Frequently asked questions
Why aren’t doors and windows subtracted?
The paper above and below a door or window is cut from full-length drops so the pattern lines up, and the pieces left over are rarely usable elsewhere. Leaving the openings in gives a margin for that waste. If your room has very large openings, ask your retailer whether you can buy fewer rolls.
What size is a roll of wallpaper?
It depends on the product. Sherwin-Williams prices US wallpaper by the single roll, about 25 usable sq ft, but sells it in double or triple rolls. A common European roll from Erismann is 0.53 × 10.05 m. Always use the size on the label of the paper you buy.
How does the pattern repeat change the result?
Each drop is rounded up to a whole number of repeats so the pattern matches across seams. A larger repeat makes each drop longer, which can leave fewer drops per roll and raise the number of rolls.
What is a drop?
One full-height strip of wallpaper, cut from the roll and hung from ceiling to floor. The number of drops around the room is the wall length divided by the roll width, rounded up.
Sources
- RollOver 27 collection – roll sizes — Erismann & Cie.. European wallpaper rolls of 0.53 × 10.05 m (also 0.75–1.06 × 25 m for wide rolls).
- How to estimate wallpaper — Sherwin-Williams. US wallpaper is priced in single rolls (about 25 usable sq ft) but sold in double or triple rolls; roll sizes vary by product.
- How to Hang Wallpaper — Brewster Home Fashions. "Measure the height of your wall and add 4 inches … You will need an extra 2 inches at the top and bottom for trimming."
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026