Wallpaper Calculator worked examples

The Wallpaper Calculator does one division and one round-up. Rolls = wall area ÷ coverage per roll, rounded up to the next whole roll. Everything else on the page is about getting those two inputs right, so the worked examples below are worth following with a pencil before you trust any answer.

Example 1: the clean case

A room has 30 square metres of wall, and each roll covers 5 square metres. 30 ÷ 5 = 6, so the answer is 6 rolls. Nothing is wasted by the rounding here, because the division comes out exact. This is the case the tool itself uses as its example, and it is the one to try first when you open the calculator: enter 30 and 5, and confirm you see 6.

Example 2: the part roll

Change the area to 32 square metres and keep the same rolls. 32 ÷ 5 = 6.4. You cannot buy 0.4 of a roll, so the answer rounds up to 7 rolls. That extra 0.6 of a roll is not waste in the usual sense — it is the margin that lets the last strip reach the corner. The same logic gives 45 ÷ 7.5 = 6 rolls exactly, while 45 ÷ 10 = 4.5, which rounds up to 5 rolls. Coverage matters as much as area: a roll that covers twice as much roughly halves the count.

Example 3: a room measured wall by wall

Two walls measure 4 by 2.7 metres (10.8 each, 21.6 together) and two walls measure 3 by 2.7 metres (8.1 each, 16.2 together), for 37.8 square metres in total. Subtract a door of 1.9 square metres and a window of 1.5 square metres: 37.8 − 1.9 − 1.5 = 34.4 square metres. At 5 square metres per roll, 34.4 ÷ 5 = 6.88, which rounds up to 7 rolls. Add one spare roll for repairs and the order is 8 rolls. If you had skipped the subtraction, the gross figure would have given 8 rolls before any spare — the same number, but for the wrong reason, and on a bigger room the gap would have cost real money.

Frequently asked questions

Why does the answer round up instead of down?

Because a part roll cannot be bought. Rounding 6.4 down to 6 would leave the last strip short, so the calculator always rounds up to the next whole roll.

What if the division comes out exact?

Then no rounding is needed: 30 ÷ 5 = 6 rolls, and 45 ÷ 7.5 = 6 rolls. The answer is exact only when the area is a whole multiple of the coverage.

Where do I find the coverage per roll?

On the roll label, given as square metres per roll. Use the figure for the exact roll you are buying, since coverage varies between products.

Wallpaper Calculator explained with worked examples