How to Calculate How Much Wallpaper You Need to Decorate a Room

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Wallpaper rolls typically measure 33′ (10m) long and 21″ (535mm) wide. If the room you’re decorating has a ceiling height of 9′ (2760mm) you’ll get three drops of wallpaper per roll.

Allow a few inches per cut length for trimming the top and bottom off each strip. Allow more if the wallpaper has a large pattern repeat.

To calculate how many wallpaper rolls you need, measure the walls of the room. In a rectangular room, you only need to measure two walls because opposite walls are the same length. You could measure the room on your own, but it’s easier, quicker and more reliable if somebody helps you.

Make a note of all the measurements, rounding up to the nearest inch. Now divide the total by 21″ or 535mm.

This figure tells you how many drops of wallpaper you need.

If you get three lengths from each roll divide the number of drops by three to calculate how many rolls you need.

The final calculation

  1. The walls measure 756″ (18900mm) in total and the ceiling height is 9ft (2760mm) allowing three drops from each roll
  2. 756″ (18900mm) ÷ 21″ (535mm) = 36 drops of wallpaper
  3. 36 drops of wallpaper ÷ 3 drops per roll = 12 rolls

Based on this calculation I would purchase 13 rolls of wallpaper which includes one spare roll for any mishaps etc.

It’s always better to have too much wallpaper

Always buy an extra roll of wallpaper in case of mistakes or you need to make repairs in the future. I don’t deduct too much paper for doors and windows from the total as it’s always better to have more than you need. Most DIY stores will credit you for any rolls you return. And there’s nothing worse than the store not having any stock of your chosen wallpaper should you run short.

Planning where to start the wallpapering depends on the room itself. If you have a main feature in the room such as a fireplace then this is your starting point. (this applies more to patterned paper, but it is something I have always done regardless of the paper being used).

The first strip of wallpaper you hang should be central to the fireplace and needs to be perfectly vertical (this is where the plumb line is invaluable) as this strip determines how straight the other strips will be.

Make sure you buy wallpaper rolls with the same batch number

When you buy your chosen wallpaper, be sure to check the batch numbers and/or colour number codes on each roll are the same. The reason for doing this is to ensure all rolls have the same pattern and colouring. Two rolls with different batch numbers may vary slightly because they were made at a different time, hence the term ‘batch’.

This doesn’t apply to lining paper, by the way.

Online wallpaper calculators

I appreciate this is a rather old-school way of working out how much wallpaper you need to decorate a room, but it still works.

If you prefer to use an online wallpaper calculator that does all the working out for you, here are some worth checking out.