How much wallpaper do I need? A plain guide

Buying too little wallpaper is the most common mistake we see, and it is the most expensive one, because the batch you bought may be sold out by the time you go back. Buying way too much wastes money. The good news is the maths is simple once you know the two numbers that matter: the size of your walls, and the pattern repeat on the paper you have chosen. Here is how we work it out in the shop.

The short version

Measure the width of every wall you are papering and add them together. Measure the height from skirting to ceiling. Multiply the total width by the height to get the area in square metres. Then divide by the usable area of one roll, and round up. A standard UK roll is about 10.05m long and 0.52m wide, which is roughly 5.2 square metres on paper. In practice you get less usable paper than that once you allow for trimming and pattern matching, so most rooms work out at one roll for every 4 to 4.5 square metres of wall.

Why the pattern repeat changes everything

Every patterned wallpaper has a repeat, which is the vertical distance before the design starts again. You will find it on the product page, listed in centimetres. A small repeat of 5cm wastes almost nothing. A large repeat of 50cm or more means you cut and discard up to half a metre at the top of most drops so the pattern lines up with the one next to it. The bigger the repeat, the more rolls you need for the same wall.

There are two main match types. A straight match lines the pattern up at the same height across both edges. An offset or half-drop match steps the pattern down by half the repeat on the next length, which can waste a little more. Plain papers and random-match designs have no repeat to worry about, so they go the furthest.

A worked example

Say you are papering a chimney breast and the two walls either side. The three sections add up to 6 metres wide. The ceiling is 2.4 metres high. That is 6 times 2.4, which is 14.4 square metres of wall.

First work out how many full drops you get from one roll. A 10.05m roll cut into 2.4m lengths gives you four drops, with a bit left over. Each drop is 0.52m wide, so one roll covers about 2.08 metres of wall width. To cover 6 metres of width you need 6 divided by 2.08, which is just under three rolls. Buy three.

Now add the pattern repeat. If the paper has a 50cm repeat, you lose up to half a metre off the top of most drops to make the pattern align. That can drop you from four usable drops per roll to three. In that case the same wall needs four rolls, not three. This is exactly why two papers on the same wall can need different quantities.

A large floral like Allure is a good example of why the repeat matters. The bigger the motif, the more you trim to line it up, so a paper like this needs the extra roll the maths above warns about. Check the repeat on its product page before you order, and zoom in on the detail photos so you can see the scale clearly.

The rules we never break

• Always round up to the next whole roll. You cannot buy half a roll, and you want a little spare for mistakes and future repairs.

• Buy all your rolls in one go, from the same batch. The batch number is printed on the label. Colour can shift very slightly between batches, and that shift shows on a finished wall.

• Keep one spare roll if the design is being discontinued. A scuff or a leak years later is easy to patch if you have the matching paper put away.

• Measure twice. Doors and windows do reduce the area, but only deduct them if they are large. A standard door is worth ignoring, because the offcuts rarely line up neatly enough to reuse.

Check the detail before you commit

Before you order rolls, spend a few minutes on the product page. Every design has large, zoomable detail photos and room-set images, so use them to study the pattern scale and colour, because both read completely differently at home than on a small screen. Each product also lists the pattern-repeat figure, which is the number that drives the maths above, so note it down before you do the sums.

When you are ready, you will find the repeat and roll size listed on every design in the wallpaper collection. Pick the paper, study the detail photos and the repeat figure, do the measuring, and round up. If you get stuck on an awkward room, send us the measurements and we will work the rolls out with you.