What this calculator works out

This calculator works out how many drops of wallpaper a roll yields at your wall height, how many drops the room perimeter needs, and therefore how many rolls to buy.

The pattern repeat is the field that catches people out. A large repeat can cut the number of usable drops per roll by a quarter or more, and the effect is not obvious until you are halfway through hanging.

Enter your details

Room perimeter (m)

Wall height (m)

Roll length (m)

Roll width (m)

Pattern repeat (m)

Your result will appear here.

Before you order

Plan of a 4.2 m by 3.1 m room. The perimeter is measured straight across the door and the window rather than around them, giving 14.6 m. Deducting openings is the usual way to end up a roll short.

Measure the perimeter as the total distance around all walls, including across doors and windows. Openings rarely save a full drop and the offcuts are needed above and below.
Measure wall height at several points. Older rooms vary by several centimetres, and you must plan for the tallest.
A standard UK roll is 10.05 m long and 0.53 m wide. Some designer and imported papers differ, so check.
The pattern repeat is printed on the label. Straight match uses the repeat as given; offset or drop match effectively uses half the repeat per drop but wastes differently.

Batch numbers matter more than they sound

Wallpaper is printed in batches and colour varies slightly between them. Rolls from different batches hung side by side show a visible shade difference under raking light. Buy all your rolls at once, check the batch numbers match, and buy the spare roll then rather than later.

How this calculator works

Drops per roll, drops needed, then rolls:

Drop length = wall height + pattern repeat
Drops per roll = roll length ÷ drop length, rounded down
Drops needed = perimeter ÷ roll width, rounded up
Rolls = drops needed ÷ drops per roll, rounded up

Both roundings go against you, which is correct — part of a drop is no use, and part of a roll cannot be bought.

Adding the full repeat to every drop is a conservative approach. In practice a skilled hanger can nest some drops to waste less, but planning on that and being wrong means a second batch.

Worked example: a 16 m perimeter

Using the default figures — 16 m perimeter, 2.4 m walls, standard 10.05 m by 0.53 m rolls, no pattern repeat:

Drops per roll: 10.05 ÷ 2.4 = 4.19, so 4 full drops
Drops needed: 16 ÷ 0.53 = 30.2, so 31 drops
Rolls: 31 ÷ 4 = 7.75, so 8 rolls

Now add a 0.5 m pattern repeat. The drop length becomes 2.9 m, which yields only 3 drops per roll, and the same 31 drops now need 11 rolls. A patterned paper has increased the order by nearly 40% without changing the room at all — which is why the repeat is worth checking before falling in love with a design.

Common mistakes

Deducting doors and windows from the perimeter. The offcuts are needed above and below them.
Ignoring the pattern repeat. It can add several rolls to a modest room.
Measuring height at one point only. Plan for the tallest measurement.
Buying rolls from different batches. The shade difference will show.
Ordering exactly enough. Always buy one spare roll from the same batch.

Frequently asked questions

Should I deduct doors and windows?

Generally not from the perimeter. You still need a drop above a door and usually short drops below a window, and those come from the same rolls. Deducting a full drop for a standard door is the sort of optimisation that leaves you one roll short. Very large openings such as patio doors are the exception and can reasonably be subtracted.

What is the difference between straight match and offset match?

Straight match repeats horizontally, so each drop starts at the same point in the pattern and adjacent drops align directly. Offset or drop match staggers the pattern between drops, usually by half the repeat, so the design flows diagonally. Offset match often wastes less overall because alternate drops can be cut from the same length, but it is harder to hang.

How many rolls spare should I buy?

One, from the same batch, is the usual advice. It covers a mis-cut, a damaged drop and any future repair. Wallpaper patterns are frequently discontinued, and matching a batch years later is close to impossible, so the spare roll is cheap insurance.

Do I need lining paper?

It is worth it on uneven walls, on previously painted surfaces, and under thin or delicate papers. It gives a uniform absorbent surface, hides minor imperfections and improves adhesion. Hang it horizontally so the joints do not coincide with those of the finish paper.

Is what I enter stored?

No. Room and roll measurements are processed in your browser and never transmitted or retained.

Related tools

References

GOV.UK — product safety and labelling requirements for decorative materials
Health and Safety Executive — safe working at height when decorating

Sources are checked at publication and can change — how I choose and check references.