What it works out
This works out how many rolls of wallpaper a room needs, and how many packets of paste to hang them. It counts the paper the way a decorator does: in drops, the lengths you cut from a roll to run from the ceiling to the skirting.
Counting drops rather than dividing the wall area by the roll's area matters, because the offcut at the end of each roll is usually too short for another drop, and a pattern repeat makes every drop longer than the wall is high.
How it works
Give the room's length and width, or each wall's width. The calculator works out how much width there is to paper, taking off each door's width. Windows stay in, because they still need paper above and below them.
That width divided by the roll's width gives the number of drops. Each drop is the wall's height plus a trimming allowance, rounded up to whole pattern repeats, plus half a repeat more for an offset match. From the roll's length it then works out how many whole drops come out of one roll.
The waste allowance is added to the drops, and the drops are divided into rolls. Paste comes last, as a number of packets from the rolls each packet hangs.
A worked example
A room 4 m by 3 m, papered 2.4 m from the skirting to the ceiling, with 1 door. Rolls of 10.05 m by 53 cm, a plain paper with no repeat.
- Round the room: 2 × (4 m + 3 m) = 14 m
- 14 m − 1 door × 0.76 m = 13.24 m to paper
- 13.24 m ÷ 53 cm wide → 25 drops
- Each drop: 2.4 m plus a trimming allowance = 2.5 m
- 10.05 m roll ÷ 2.5 m → 4 drops a roll
- 25 drops + 10% for waste → 28 drops
- 28 drops ÷ 4 a roll → 7 rolls
- 7 rolls ÷ 5 a packet → 2 packets of paste
The result
- Wallpaper7 rolls
- Paste2 packets
These are the calculator's own figures for these measurements, with 10% for waste. Change any of them above and it works it out again.
Common mistakes
- Dividing the wall area by the roll's area. It ignores the short offcut left on every roll and the pattern repeat, and usually comes out a roll or two short.
- Ignoring the pattern repeat. A large repeat can mean only three drops from a roll where a plain paper gives four. Check the label.
- Mixing batch numbers. Rolls from different batches can differ slightly in shade. Check the batch number on every roll and buy one more than you think, from the same batch.
- Measuring the height from the floor. Paper runs from the top of the skirting to the ceiling or the coving. Measure that height.
Questions people ask
How many rolls of wallpaper do I need?
Work out how many drops the room needs, how many drops each roll gives, and divide. The calculator does this from the room's size, the wall height, the roll size and the pattern repeat.
What is a pattern repeat?
The distance before the pattern starts again down the roll. It's printed on the label. Each drop must start at the same point in the pattern, so a long repeat wastes more paper.
What's the difference between a straight and an offset match?
With a straight match the pattern lines up across drops at the same height. With an offset (or half-drop) match each drop is shifted by half a repeat, which uses more paper.
Should I take windows off?
No. You still need paper above and below a window, and the pieces around it rarely come from offcuts. Doors are taken off, because they run almost floor to ceiling.
How much paste do I need?
A packet of paste usually hangs several rolls; the number is on the packet. The calculator divides the rolls by that number, which you can change under More options. Heavy papers may need a ready-mixed adhesive instead.