The repeat and match type are printed on the roll label.
How the wallpaper calculator works
Wallpaper is hung in vertical strips called drops. Each drop runs from ceiling to skirting plus a little extra for trimming. A roll can only give whole drops: if a roll is 33 feet long and each drop is 100 inches, you get three drops and the remaining 96 inches is too short for another. That is why WallpaperCalc counts drops instead of dividing wall area by roll area. Area-based estimates often come out short.
The steps
First the total wall width is divided by the roll width to get the number of drops, rounded up. Doors save about one drop each and windows about half a drop, since you still need short pieces above and below. Next the drop length is the wall height plus 4 inches, or 10 cm, for trimming. For patterned paper the drop is rounded up to a whole number of pattern repeats, and a half-drop match adds half a repeat more. Finally the roll length is divided by the drop length to see how many drops each roll gives, and the drop count is divided by that to get rolls.
Roll sizes
In the US, wallpaper is usually priced per single roll but sold in double rolls about 20.5 inches wide and 33 feet long. Some American papers are 27 inches wide. In the UK and Europe a standard roll is 53 cm wide and 10.05 m long, and wide rolls of 70 cm are common. Peel and stick rolls are often shorter, so check the label.
Buying tips
Buy all rolls with the same batch or lot number, because colours vary slightly between print runs. Add one extra roll for mistakes and future repairs. Measure each wall separately if the room has alcoves or a chimney breast. Everything is calculated in your browser.
Frequently asked questions
What is a straight match?
The pattern lines up horizontally on every drop.
What is a half-drop match?
Every other drop is shifted down by half the repeat.
What is a random match?
No alignment needed, so there is very little waste.
Is WallpaperCalc free?
Yes, with no sign-up or ads.
Are my measurements saved?
Yes, in this browser only.