wallpaper calculator — the complete guide

This guide covers the whole job, from tape measure to order, using the Wallpaper Calculator's own method throughout: rolls = wall area ÷ coverage per roll, rounded up. If you read only one post in this set, read this one, because it joins the measuring, the formula and the buying decisions into one sequence.

Measure and subtract

Measure every wall, length times height, and add the results. A room with two walls of 4 by 2.7 metres and two walls of 3 by 2.7 metres has 21.6 + 16.2 = 37.8 square metres. Subtract every opening: a door of 0.9 by 2.1 metres is 1.9 square metres, and a window of 1.5 square metres leaves 37.8 − 1.9 − 1.5 = 34.4 square metres. If your measurements are in square feet, convert first: square metres = square feet ÷ 10.764, so 300 square feet is 27.9 square metres. Measure height at two points on each wall if the ceiling is uneven, and use the larger height — a strip cut short cannot be stretched.

Read the label, divide, round up

Find the coverage on the roll label, in square metres per roll. Divide the net area by that figure and round up to the next whole roll, always. For the room above at 5 square metres per roll: 34.4 ÷ 5 = 6.88, so 7 rolls. For a larger room of 60 square metres at the same coverage: 60 ÷ 5 = 12 rolls exactly. For a different roll covering 7.5 square metres: 45 ÷ 7.5 = 6 rolls, while the same area at 10 square metres per roll is 45 ÷ 10 = 4.5, rounded up to 5 rolls. Coverage is not a minor detail — it changes the order by whole rolls.

Buy, with pattern and spare in mind

The calculated number is the minimum. Two decisions sit on top of it. First, a large pattern repeat wastes paper at every join, because each strip must start at the same point in the pattern, so add one extra roll when the repeat is large. Second, buy one spare roll from the same batch when you can, for torn strips during hanging and for later repairs, since a later batch can differ slightly in colour. For the room above, that means 7 calculated rolls, 8 with a spare, or 9 if the pattern is also large. Finally, keep the batch number: if you ever need more, the same batch is the only way to guarantee the same colour.

Frequently asked questions

How do I measure a room for wallpaper?

Multiply each wall length by its height, add the walls, then subtract every door and window.

What is the wallpaper formula?

Rolls = wall area ÷ coverage per roll, rounded up to the next whole roll.

How many extra rolls should I buy?

One spare from the same batch, plus one more if the pattern repeat is large.

More guides on the Wallpaper Calculator

• How to use the Wallpaper Calculator — step by step
• Wallpaper Calculator explained with worked examples
• Wallpaper Calculator formula — how it actually works
• Wallpaper Calculator for beginners — start here
• Common mistakes people make with the Wallpaper Calculator
• Wallpaper Calculator vs doing it by hand — which is faster?
• How to get an accurate result from the Wallpaper Calculator
• Wallpaper Calculator for students — with examples
• Wallpaper Calculator for homeowners and DIYers