Wallpaper calculator

How the calculator works

Wallpaper is sold by the roll, but you hang it by the drop — one vertical strip from ceiling to skirting. The calculator therefore does three things, in that order.

First it divides the wall run by the roll width (0.53 m on a standard European roll) and rounds up. A 12 m run needs 23 drops, not 22.6. You cannot hang six-tenths of a strip.

Second it decides how long each drop must be. Height plus trim is the hung length. If the paper has a pattern, that length is then rounded up to the next whole repeat so the motif lines up from drop to drop. Half-drop papers add half a repeat on every other drop.

Third it turns those lengths into rolls in two ways. The headline number — rolls to buy — is how many rolls you need if each roll only yields whole drops. Leftover paper on a roll cannot be taped onto the next drop; the seam would show. A second figure, the theoretical minimum, divides the total length by the roll length as if offcuts could be spliced. Shop calculators often show something closer to that second number. The gap between them is the reason this tool exists.

Free, straight, and half-drop

The match is printed on the label, usually as a small icon next to the repeat in centimetres. Using the wrong mode is the most common way to buy too little paper.

Free match (sometimes called a random match) has no motif that must line up across the seam. Each drop is simply wall height plus your trim allowance. Plain textures, many grasscloths, and some small speckles are free match.

Straight match lines the motif up at the same height on every drop. If the hung length is 2.50 m and the repeat is 0.64 m, each drop is cut at 2.56 m — four repeats — so the leftover 0.06 m is waste you planned for, not a surprise on the last wall.

Half-drop (also called offset match) shifts every other drop by half a repeat. The first, third, and fifth drops cut at the straight-match length; the second, fourth, and sixth are half a repeat longer. Designers use it so the eye does not read a grid of identical flowers. The longer drops set how many strips you can take from one roll, which is why a half-drop paper can need more rolls than a straight-match paper with the same repeat.

Why a pattern repeat costs rolls

A 0.53 × 10.05 m roll holds 10.05 m of paper. That is a fact about the cylinder, not about your room. The useful question is how many whole drops fit on that cylinder.

Take a 12 m run, 2.40 m ceilings, 0.10 m of trim, and a 0.64 m straight match — a common living-room wall in a panel-built flat. The hung length is 2.50 m; after matching, each drop is 2.56 m. Twenty-three drops need 58.88 m of paper. 58.88 ÷ 10.05 is 5.86, which a length-only calculator rounds to 6 rolls.

You cannot get that 5.86. Each roll yields floor(10.05 ÷ 2.56) = 3 drops, and 0.37 m of unusable offcut. Twenty-three drops at 3 per roll is 8 rolls. The extra two rolls are not padding we added for luck — they are the paper you will physically leave on the tube.

That is also why two papers in the same shop can disagree. A free-match texture on the same wall needs 2.50 m drops, 4 per roll, and 6 rolls. Same room, same roll size, two extra rolls because of the motif.

Worked examples

Both examples use the same room: 12 m of wall, 2.40 m high, 0.10 m trim, a 0.53 × 10.05 m roll, and a 0.64 m repeat. Only the match changes. The calculator above is pre-filled with the straight-match case so you can flip the radio and watch the numbers move.

How to measure, and what to buy

Measure each wall at the height you will paper, not along the skirting — older buildings are not square. Add the widths. Do not subtract doors and windows yet; the strips that run beside a door still need a full drop of paper, and the offcuts rarely become a clean panel elsewhere. If a wall is almost all glass, measure that wall on its own and decide by eye.

Ceiling height in Estonia is not one number. Soviet-era panel flats (khrushchyovka and later large-panel series) often sit around 2.50 m to the slab; after a floating floor and a lowered ceiling you may have 2.40 m of paintable wall. Newer apartments and renovated wooden houses more often land between 2.60 m and 2.70 m. A 10 cm change in height can cost a whole extra drop per roll once a large repeat is in play — type the real height.

The 0.53 × 10.05 m roll is what Bauhaus, K-Rauta, and most Estonian DIY counters sell as a standard European roll. Designer and non-woven collections sometimes ship 0.70 m or 10.00 m; open the roll-size panel and type what is on the label. American 27-inch rolls are a different product and will throw the drop count off.

Order every roll from the same dye lot. If the shop is short, wait. Buy one spare if the paper is a special order or if you are hanging an old, out-of-square room — the calculator already counts matching waste, but it cannot see a bay window.