Get an accurate Wallpaper result

An accurate wallpaper result is decided before you open the calculator. The division is exact; the inputs are where accuracy lives or dies. Work through this checklist in order and the result will be as accurate as the job allows.

Measure twice, and measure the right things

Measure every wall separately, length times height, and write each figure down rather than carrying it in your head. Measure height at two points on each wall: where a ceiling slopes or a floor is uneven, the larger height is the one to use, because a strip cut short cannot be stretched. Then subtract openings exactly, not approximately: a door of 0.9 by 2.1 metres is 1.9 square metres, and rounding it to 2 square metres on every opening adds up across a house. The room example used throughout this set — 37.8 square metres of wall, minus a 1.9 square metre door and a 1.5 square metre window, giving 34.4 square metres — is accurate only because each figure was measured, not guessed.

Use the real roll label, then verify

Coverage varies between products, so use the figure on the exact roll you are buying, in square metres per roll. A guessed coverage of 5 when the real roll covers 7.5 changes a 45 square metre room from 9 rolls to 6 — a three-roll error from one guessed number. Once you have the answer, verify it by hand: 34.4 ÷ 5 = 6.88, rounded up to 7 rolls. Then run a second version with a slightly different area, for example 32 square metres, and confirm the calculator gives 32 ÷ 5 = 6.4, rounded up to 7 rolls. If either check fails, an input is wrong, and the input to recheck first is the one you estimated rather than measured.

Frequently asked questions

What is the biggest source of wallpaper inaccuracy?

Guessed inputs, especially coverage. Use the figure on the exact roll label, not a remembered number.

Should I measure height at more than one point?

Yes, where a ceiling or floor is uneven. Use the larger height, since a short strip cannot be stretched.

How do I verify a wallpaper result?

Divide by hand: net area ÷ coverage, rounded up. 34.4 ÷ 5 = 6.88, so 7 rolls.

How to get an accurate result from the Wallpaper Calculator