Its a really common mistake to buy too little wallpaper. The next really common mistake it to buy more rolls which do not have the same batch number as the first rolls. The paper looks pretty much the same, so what's the problem?
Wallpaper is printed in batches. At the end of each batch, the ink colours are remixed and the print rollers realigned. This can mean that the colours are slightly different which will be noticeable when the rolls are side by side on a wall. It can also mean that the pattern is shifted to one side, making pattern matching extremely difficult. There are a few golden rules to remember when buying wallpaper.
Calculate the wall size accurately.
For each wall, multiply the width of the wall by the height. Don't take away for doorways or windows. These sometimes take more paper, not less.
Check the pattern repeat.
On each roll, there will be a symbol to tell you the type of pattern (random, straight or offset match) and how frequently the pattern repeats itself. The bigger and more complex the repeat, the more paper will be used. Add extra for damages or mistakes
Sometimes there will be a printing error on the roll, or a scratch or tear meaning you have to throw some away. Sometimes you might just measure or cut wrong. You can usually return any rolls you haven't used. Use an online calculator to double check your calculations!
This one is good https://www.amara.com/wallpaper/calculator
Buy local if you can
They should be able to help you calculate how much you need and it really helps if you have to go back and get more with the same batch number, or return rolls you didn't need.
Uh oh. I already bought the rolls and there aren't enough!
If you have bought locally you can usually go back to the shop and buy more. Check the batch numbers match the rolls you already have!
If you can't do this, or the batch numbers don't match, return the rolls you already have, and buy the right amount.
I'm stuck with batch number that don't match!
You could use different batches on different walls. You shouldn't notice subtle changes in colours.
I don't have enough paper and I can't buy more
You can wallpaper just one or 2 walls as feature walls, or choose smaller walls for a feature wall. Or, you can put additional cuts in the lengths of paper to make it go further. With an offset match paper you can have 2 rolls on the go which results in slightly less waste but can get confusing!