Wallpaper Calculator
How many rolls the room needs, from the wall size, roll size and pattern repeat.
How rolls are counted
Wallpaper hangs in vertical strips. Each strip must be the wall height plus one pattern repeat (every strip after the first is trimmed to match the pattern), so a 33 ft roll yields floor(33 / strip length) usable strips. Strips needed is the total wall width divided by the roll width, rounded up. 40 ft of wall at 8 ft high with a plain 21-inch paper: 23 strips, 4 per roll, 6 rolls.
Buying advice
Not subtracting doors and windows is deliberate: the offcuts around them are rarely reusable, and the margin covers mistakes. Large repeats are expensive; a 24-inch repeat on an 8-foot wall wastes a fifth of every roll. Buy all rolls from the same batch number, and one spare beyond the calculation if the paper may be discontinued; matching a batch later is nearly impossible.