How Much Wallpaper You Actually Need

Two rooms of identical size can need noticeably different amounts of wallpaper. The variable is not the walls. It is the pattern.

The calculation

1. Drops needed. Room perimeter divided by roll width, rounded up.
2. Length per drop. Wall height, plus the pattern repeat allowance, plus about 10 cm for trimming.
3. Usable drops per roll. Roll length divided by length per drop, rounded down. A partial drop is waste.
4. Rolls. Drops needed divided by drops per roll, rounded up.

Step three is where the damage happens, and it is why the answer is not a smooth function of the numbers.

Why repeat costs so much

A standard 10.05 m roll against a 2.4 m wall:

Plain paper. Each drop needs 2.5 m. Four fit in a roll, with 0.05 m left over.

64 cm repeat. Each drop needs up to 3.14 m. Three fit in a roll, and 0.63 m is wasted.

Same room, same roll, 33% more rolls. Nothing about the walls changed.

This is worth knowing before you fall in love with a pattern. A large repeat on a tall wall adds meaningfully to the cost, and the repeat figure is printed on the label precisely so you can check.

The three match types

Type	How it aligns	Waste
Free match	No alignment needed	Minimal
Straight match	Same height on every drop	Up to one repeat per drop
Offset or drop match	Alternate drops staggered by half a repeat	Most, though often looks better

Free match papers are usually textures, stripes or deliberately random designs. They are considerably more forgiving for a first attempt and cheaper to hang because so little is thrown away.

If this is your first time papering a room, the match type is a bigger factor in how it goes than the price of the paper.

Doors and windows

Do not simply subtract their area.

A window in the middle of a wall still needs paper above and below it, and those offcuts rarely combine into a usable full drop. Subtracting the full area consistently leads to under-ordering.

A reasonable rule is to credit roughly half a drop for a standard door and a quarter for a large window. Ignore small windows entirely.

Under-ordering is far more expensive than over-ordering, for a reason that has nothing to do with money.

Batch numbers matter more than with paint

Wallpaper is printed in batches, and shade varies between them. Sometimes obviously.

Two adjacent drops from different batches show a visible line down the wall in daylight. You will see it every day for as long as the paper is up.

• Buy every roll at once
• Check the batch numbers on the labels match before leaving the shop
• Buy one spare from the same batch
• If you must mix batches, use the odd ones on a separate wall rather than alongside

This is the single most common expensive mistake in wallpapering, and it is entirely avoidable by reading a label.

Practical points

Start from a corner near the door. The pattern will not match where it eventually meets itself. Put that mismatch in the least visible place.

Hang the first drop against a plumb line, not the corner. Walls are rarely straight and the error compounds across the room. By the fourth wall a small lean becomes obvious.

Cut all the drops for a wall before pasting, checking the pattern aligns as you go. It is much easier to discover a problem with dry paper on the floor.

Leave 5 cm spare at each end for trimming.

Check whether the ceiling is level before assuming a drop can be cut square. Most are not.

The one number to look up first

Before anything else, find the pattern repeat on the label and put it into the wallpaper calculator along with your wall height.

If it tells you the repeat is costing extra rolls, that is worth knowing while you can still choose a different paper. Afterwards it is just an expense.