Wallpaper Calculator for students — with examples

Wallpaper is a good classroom example because it uses three ideas together: area, division, and rounding up for a real-world reason. The formula is rolls = wall area ÷ coverage per roll, rounded up. The rounding is not a convention — it is forced by the fact that wallpaper is sold by the roll, so a part roll cannot be bought.

Three worked problems

Problem 1: a room has 20 square metres of wall and each roll covers 5 square metres. 20 ÷ 5 = 4 rolls exactly. Problem 2: a room has 27 square metres of wall with the same rolls. 27 ÷ 5 = 5.4, which rounds up to 6 rolls. Problem 3: a room measures two walls of 4 by 2.7 metres (21.6 square metres) and two walls of 3 by 2.7 metres (16.2 square metres), for 37.8 square metres, minus a door of 1.9 square metres and a window of 1.5 square metres, giving 34.4 square metres. At 5 square metres per roll, 34.4 ÷ 5 = 6.88, which rounds up to 7 rolls. Notice how problem 3 is just problems 1 and 2 with the measuring step added: area first, then division, then round-up.

What to watch for in exam-style questions

First, always subtract openings before dividing; a question that gives a door and a window expects them subtracted, and skipping them is the most common lost mark. Second, watch the units: if the area is given in square feet, convert first with square metres = square feet ÷ 10.764, so 300 square feet becomes 27.9 square metres, and 27.9 ÷ 5 = 5.58, rounded up to 6 rolls. Third, never round down or to the nearest: 5.4 rounds up to 6, not down to 5 and not to the nearest whole roll, because the nearest rule would leave the room short. Try each problem in the calculator and confirm the answers: 4, 6 and 7 rolls.

Frequently asked questions

Why do we round up for wallpaper?

Because wallpaper is sold by the roll. A result of 5.4 rolls means 6 rolls must be bought, or the last strip will be short.

How do you find wall area?

Multiply each wall length by its height, add the walls, then subtract doors and windows.

How do you convert square feet to square metres?

Divide by 10.764. 300 square feet is about 27.9 square metres.