Wallpaper Calculator

What is a wallpaper calculator?

A wallpaper calculator tells you how many rolls of wallpaper to buy to cover a wall. You enter the wall’s width and height, the width and length of one roll, and a wastage allowance, and it returns the total wall area and the number of rolls you need. Working this out in advance means you can order everything in one go, ideally from the same batch, instead of running short halfway through and hunting for a matching dye lot later.

Wallpaper is sold by the roll, and a roll is much longer than it is wide. You hang it in vertical drops (also called strips) that run from ceiling to skirting, so the real question is not “how much area does a roll cover?” but “how many full-height drops can I cut from one roll, and how many drops does the wall need?”

How does it work?

First the calculator finds the wall area. A rectangular wall that is $W$ wide and $H$ high has an area of:

Then it works in drops rather than area, because a printed wallpaper cannot be pieced together freely. Each drop is one roll-width wide, so the number of drops needed across the wall is the wall width divided by the roll width, rounded up to a whole drop:

where $w$ is the roll width. Each roll yields a whole number of full-height drops. Because every drop must be a little longer than the wall to allow for trimming and pattern matching, the usable drop length is the wall height inflated by the wastage percentage $p$. The number of drops you can cut from one roll of length $L$ is:

rounded down, because a part-length offcut is not tall enough for a full drop. Finally, the number of rolls is the drops you need divided by the drops each roll provides, rounded up:

Worked example

Take a wall 5 m wide and 2.5 m high, papered with a standard roll 0.53 m wide and 10 m long, allowing 10% for wastage.

• Wall area: $A = 5 \times 2.5 = 12.5 \text{ m}^2$.
• Drops needed: $\left\lceil 5 / 0.53 \right\rceil = \left\lceil 9.43 \right\rceil = 10$ drops.
• Drops per roll: each drop needs $2.5 \times 1.1 = 2.75 \text{ m}$ of roll, so $\left\lfloor 10 / 2.75 \right\rfloor = \left\lfloor 3.64 \right\rfloor = 3$ drops per roll.
• Rolls: $\left\lceil 10 / 3 \right\rceil = \left\lceil 3.33 \right\rceil = 4$ rolls.

So this wall needs 4 rolls. Notice you cannot just divide the wall area (12.5 m²) by the roll area (5.3 m²), which would suggest fewer than 3 rolls — the offcut at the bottom of each roll is wasted, and rounding drops down then rolls up captures that loss.

For a smaller wall 4 m wide and 2.4 m high with the same roll and wastage: the area is $4 \times 2.4 = 9.6 \text{ m}^2$, you need $\left\lceil 4 / 0.53 \right\rceil = 8$ drops, each roll gives $\left\lfloor 10 / (2.4 \times 1.1) \right\rfloor = 3$ drops, so you need $\left\lceil 8 / 3 \right\rceil = 3$ rolls.

Practical notes

• Wastage matters more with large patterns. A plain or random-match paper wastes little, so 10% is generous. A large repeating motif that must line up between drops can waste 15–20% or more, because you discard part of each drop to keep the pattern aligned. Raise the wastage percentage to match your paper’s pattern repeat.
• The estimator treats the wall as a solid rectangle. It does not subtract doors and windows. Leaving them in is deliberate — you almost always paper past an opening and trim, and the offcuts rarely form a full extra drop. Only deduct very large openings by hand.
• Buy all rolls from the same batch. Colour can shift slightly between print runs, so order the full count (and ideally one spare roll) at once and check the batch number on every roll.
• Round only at the end. For multiple walls, add up the drops across all walls first, then divide by drops per roll — rounding each wall separately buys more rolls than you need.
• Related tools. Estimate paint for the same room with the paint calculator, plan wall panels with the drywall calculator, or double-check a surface with the square footage calculator.

Frequently asked questions

How many rolls do I need for a 5 m by 2.5 m wall? With a standard 0.53 m × 10 m roll and 10% wastage, you need 4 rolls — 10 drops across the wall, 3 full drops per roll.

Can’t I just divide the wall area by the roll area? No. That undercounts, because the leftover length at the end of each roll is too short for a full-height drop and is wasted. Counting whole drops per roll and rounding up gives the honest figure.

What wastage percentage should I use? Use about 10% for plain or free-match papers, and 15–20% for papers with a large pattern repeat that must be matched between drops.