Wallpaper calculator

Rolls to order, worked out from the pattern repeat rather than the wall area — because on patterned paper the repeat, not the room, decides how much you waste.

Walls

Total wall run Add up the width of every wall you are papering. Measure round the room, including doors and windows.

Wall height Floor to ceiling, at the tallest point.

Trim allowance per drop Cut off top and bottom so the drop can be slid into position. 100 mm total is standard; allow more on an uneven ceiling.

Deduct full-height openings Only tick this for patio doors, an archway or a wall of glazing. A normal door or window should not be deducted — the offcuts above and below them are what you paper those areas with.

The paper

Roll size

Roll width

Roll length

Pattern match

Pattern repeat Printed on the roll label. Enter 0 for a plain or free-match paper.

Add one spare roll from the same batch

Costs (optional)

Currency

Price per roll

Per paste tub

Rolls to order

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Drops needed—
Cut length per drop—
Full drops per roll—
Offcut left on each roll—

Also needed

Paste—
Area covered—
Area you are buying—

How this calculator works

Wallpaper is bought in drops, not in square metres

A roll is a fixed length of a fixed width. You cut it into vertical strips — drops — and hang them side by side. So the question is never "how many square metres is the room", it is "how many drops do I need, how long must each one be, and how many of those fit in a roll". Area-based calculators get patterned paper badly wrong because they ignore the middle question entirely.

The pattern repeat sets the cut length

On a patterned paper, every drop has to start at the same point in the pattern as its neighbour. You cannot cut a drop to exactly the wall height — you must cut it to a whole number of pattern repeats, then trim. That is where the waste comes from, and it is entirely determined by the relationship between your wall height and the repeat:

cut length = ceiling( (wall height + trim) ÷ repeat ) × repeat

A 2.4 m wall with a 100 mm trim allowance needs 2.5 m of usable paper. With a 530 mm repeat that rounds up to 5 repeats — 2.65 m per drop, so 150 mm goes in the bin off every single drop. With a 640 mm repeat the same wall needs 4 repeats, 2.56 m, and you waste only 60 mm. Same room, same paper price, noticeably different bill.

Half-drop patterns cost you an extra half repeat

On an offset or half-drop match, alternate drops start halfway through the pattern. The trade allowance is to add half a repeat to the required length before rounding up, which is what this calculator does when you select that match type. It typically costs one extra roll on an average room, and it is the single most common reason people run short.

Do not deduct normal doors and windows

This surprises people, but it is how decorators estimate. You still hang a full drop each side of a window, and the short pieces above and below it come out of the offcuts you already paid for. Deducting the opening area makes you order too little. Deduct only when an opening runs full height for a meaningful width — patio doors, an archway, a glazed wall.

Batch numbers matter more here than anywhere else. Wallpaper is printed in batches and the colour varies between them, far more visibly than tile. Two rolls from different batches hung side by side show a line down the wall in daylight. Buy every roll you need in one order, check the batch numbers match on delivery, and keep the spare.

A worked example

A 4.5 × 3.0 m room, 2.4 m high, papered on all four walls with a 53 cm × 10.05 m roll and a 530 mm straight-match repeat:

Wall run = 2 × (4.5 + 3.0) = 15 m
Drops = 15 ÷ 0.53 = 28.3 → 29 drops
Cut length = ceiling(2.5 ÷ 0.53) × 0.53 = 5 × 0.53 = 2.65 m
Drops per roll = floor(10.05 ÷ 2.65) = 3, leaving 2.1 m of offcut on every roll
Rolls = 29 ÷ 3 = 9.67 → 10 rolls, plus one spare

Note the shape of that answer: three drops per roll with 2.1 m left over. You are throwing away a fifth of every roll, and no amount of careful hanging changes it — it is fixed by the arithmetic the moment you choose that paper for that wall height.

Common questions

Where do I find the pattern repeat?

On the roll label, usually as a symbol plus a figure in centimetres. A straight-match symbol is two short horizontal lines at the same height; an offset match shows them staggered. If the label shows an arrow and no figure, it is a free match with no repeat — enter 0 and the calculator drops the rounding step entirely.

Can I use the offcuts?

Above doors and above and below windows, yes, and the calculation above assumes you will. For anything else, usually not: a 2.1 m offcut is too short for a 2.65 m drop, so it sits in the corner of the room until the job is finished. If your offcut is longer than your cut length you have made an arithmetic error somewhere.

Does a paste-the-wall paper change the quantity?

Not the number of rolls — that is set by geometry. It changes the paste: paste-the-wall products cover more area per tub because none is wasted on a pasting table, and they are much faster to hang. The roll count is identical.

Do I need lining paper?

On anything less than a smooth, sound, previously papered wall, yes. Lining paper is hung horizontally, has no pattern and no repeat, so its quantity is simply area divided by roll area plus about 10%. Hang it in the opposite direction to your finish paper so the joints never coincide.

What if the ceiling is not level?

It is not, and this is why the trim allowance exists. On a visibly sloping ceiling, raise the allowance to 150 or even 200 mm so you have room to trim each drop to the actual line. Check first with a spirit level — if the ceiling runs out by more than about 20 mm across a wall, hang to a level line rather than to the ceiling and accept the wedge at the top.

How to measure a room properly
Paint calculator — for the ceiling and the woodwork
Drywall calculator — if the walls need boarding first

Method last reviewed 2026-09-18. Estimates for planning; the roll label is the authority for repeat and match type.