Calculating Wallpaper is often not easy. We do it on a day to day basis and can sometimes be 'out' (usually too much wallpaper than too little). This is because some hangers hang in a different way to what we would. So our first piece of advice is to double check with the personal hanging - especially if it is over multiple walls.
Second piece of advice. If possible always over estimate than under. You can always on-sell left over rolls which is way less stressful than under calculating and running out of product and having an imperfect end result. IT HAS HAPPENED.
We often spend hours chasing up third party suppliers in all parts of the world to see if they have a spare batch number tucked away somewhere.
The easiest projects to calculate are one wall projects. The average wall is 2.4 high. The average pattern repeat is .53cm. So lets go with the average.
Calculating a 2.4H x 3 wide wall.
For a 2.4 ceiling height you will need to add .53cm to every drop.
2.4 + .53cm = 293cm per drop.
This means you will get 3 drops per roll (293 x 3 = 879cm out of a 10 metre roll).
Each drop is .53cm wide. 3 x .53cm = 159cm wide of cover per roll.
So if your wall is 300 cm wide you need 2 rolls to give a total of 318cm wide.
That is a nice easy wall to calculate.