How to use the Wallpaper Calculator

The Wallpaper Calculator asks for two numbers: your total wall area in square metres, and the coverage of one roll in square metres per roll. Put those two numbers in and it divides the first by the second, then rounds the answer up to a whole roll. That rounding up is the whole point — you cannot buy part of a roll, so a result of 6.4 rolls means you need 7.

Measure first, then enter

Start with a tape measure, not with the calculator. For each wall, multiply its length by its height, and add the walls together. A room with two walls of 4 metres by 2.7 metres and two walls of 3 metres by 2.7 metres has 21.6 + 16.2 = 37.8 square metres of wall. Then subtract the openings: a door of 0.9 by 2.1 metres is 1.9 square metres, and a window of 1.5 square metres brings the total to 37.8 − 1.9 − 1.5 = 34.4 square metres. That 34.4 is the figure to enter, not the 37.8 you started with.

Next, find the coverage on the roll label. It is usually given as square metres per roll, for example 5 square metres per roll. Enter that as the second number. For the room above, 34.4 ÷ 5 = 6.88, which rounds up to 7 rolls. If you had entered the gross 37.8 instead, you would have got 37.8 ÷ 5 = 7.56, which rounds up to 8 rolls — one roll bought for wall that is not there.

Read the result, then buy

The headline number is the rolls you need. Treat it as a minimum, not as an order quantity, when the pattern is large: the tool itself warns that a large pattern repeat wastes paper at every join, because each strip must start at the same point in the pattern, so one extra roll is sensible there. A spare roll from the same batch is also worth having for a torn strip or a later repair, since a later batch can differ slightly in colour.

Worked example to check against the tool: 30 square metres ÷ 5 square metres per roll = 6 rolls exactly. Change the area to 32 square metres and the same rolls give 32 ÷ 5 = 6.4, which rounds up to 7 rolls. Try both in the calculator and confirm you get 6 and then 7. If your result differs, one input differs — usually the area, the coverage, or a unit.

Frequently asked questions

What do I enter first?

Your total wall area in square metres, then the coverage of one roll in square metres per roll. The result updates as you type, so you can check each entry as you go.

Do I need to create an account?

No. Everything runs in your browser, nothing is sent anywhere, and there is no sign-up. You can run as many versions as you like.

Should I buy exactly the calculated number?

Buy the calculated number plus one spare roll if you can. A torn strip or a future repair is much easier with a roll from the same batch.

How to use the Wallpaper Calculator — step by step