Wallpaper Calculator

Wallpaper Calculator: How Many Rolls Do I Need?

Quick answer: a 12 × 10 ft room with 8 ft ceilings, one door and one window needs 8 US double rolls of plain wallpaper — 9 if you count the full perimeter with nothing deducted, and more again once a pattern repeat stretches every drop. Wallpaper is not really sold by the square foot: it is hung in full-height strips, so what matters is how many strips your walls need and how many complete drops each roll can give you. Enter your room and your roll below, and the calculator does the strip maths for you, in feet and inches or in metres.

Quick answer by room size

The table assumes 8 ft ceilings, one standard door and one standard window already deducted, US double rolls (20.5 in × 33 ft) and no pattern repeat. Those are the same assumptions the calculator below starts from, and you can change every one of them.

Room size	Rolls needed (US double)
10 × 10 ft	7 rolls
12 × 10 ft	8 rolls
12 × 12 ft	9 rolls
16 × 12 ft	10 rolls

As a rough check, most ordinary bedrooms land between seven and ten double rolls. Tall ceilings and a large pattern repeat push the number up faster than room size does, because both shorten the usable length of every roll — a 20 in repeat on a 10 ft wall can drop you from three drops per roll to two, which adds half as many rolls again.

How the strip method works

Forget wall area for a moment. Nobody hangs wallpaper by the square foot: you cut the roll into drops — full-height lengths — and hang those drops side by side as strips around the room. So the honest way to count rolls is to count strips first, then ask how many strips one roll can supply. That is all this calculator does, in five steps.

• Step 1 — perimeter: 2 × (room length + room width). This is the full run of wall you are covering, measured all the way round.
• Step 2 — take off doors and windows: subtract 3 ft (0.9 m) for each door and 3 ft (0.9 m) for each window. You do not need full strips where an opening breaks the wall, so that width comes off the run.
• Step 3 — count the strips: effective perimeter ÷ roll width, rounded up. A 20.5 in wide roll covers 20.5 in of wall per strip, so a 456 in run needs 23 strips once rounded up.
• Step 4 — work out the drop: wall height + 4 in (10 cm) of trim allowance. If the paper has a pattern repeat, the drop is rounded up to the next whole repeat so the pattern lines up from strip to strip.
• Step 5 — drops per roll, then rolls: drops per roll = roll length ÷ drop, rounded down — a part-drop is waste. Rolls = strips ÷ drops per roll, rounded up. Twenty-three strips at three drops per roll means eight rolls, and the part-used eighth roll is exactly why a spare rarely goes to waste.

Notice what is missing: total wall area. Area-based estimates — "a double roll covers about 56 sq ft, so divide your wall area by 56" — ignore the drop entirely, and they fail whenever the roll length does not divide neatly into your wall height. A room with 9 ft ceilings gets two drops from a 33 ft roll and strands nearly 15 ft of it; the area method never sees that loss, and the strip method cannot miss it. The calculator still shows the gross wall area for reference, but the roll count always comes from strips.

Wallpaper roll sizes

Rolls come in a small number of standard sizes, and the name on the shelf describes the roll, not the coverage you will actually get. These are the three sizes the calculator offers as presets.

Roll	Size	Nominal coverage
US single roll	20.5 in × 16.5 ft	≈ 28 sq ft
US double roll	20.5 in × 33 ft	≈ 56 sq ft
European roll	53 cm × 10.05 m	≈ 5.33 m²

A US double roll is not wider than a single — it is the same 20.5 in wide and simply twice as long, and it is normally sold and priced as one roll. That length is what makes it economical: at 8 ft ceilings a double roll gives three full drops, while a single gives one drop and a long offcut. European rolls are a touch wider at 53 cm and just over 10 m long. Whichever you buy, treat the printed coverage as a ceiling, not a promise: it assumes every inch of the roll lands on the wall, which trim, matching and the odd spoilt strip will never allow. If your paper is a non-standard size, choose Custom in the calculator and type in the width and length from the label.

How pattern repeat eats paper

The pattern repeat is the vertical distance after which the design starts again — printed on the label, often as a figure like 53 cm or 21 in, sometimes with the match type (free, straight or offset / half-drop). It matters because consecutive strips must start at the same point in the pattern, or the design steps visibly at every seam. You cannot cut a drop to the exact length of the wall; you must cut it to the next whole repeat at or above the length you need.

The calculator builds this in. Each drop starts as wall height plus the 4 in (10 cm) trim allowance, and if you enter a repeat, that figure is rounded up to a whole number of repeats. Take a 10 ft wall: the plain drop is 120 + 4 = 124 in. With a 20 in repeat, 124 in is not a whole number of repeats, so the drop becomes 140 in — the next multiple of 20. A 33 ft (396 in) double roll now yields two drops instead of three, and a room that needed 26 strips jumps from 9 rolls to 13. Nothing about the room changed; the repeat alone added four rolls.

Two habits keep the damage down. Cut each new drop from the roll in sequence rather than from a random offcut — offcuts often start at the wrong point in the repeat, and are really only good for the short pieces above doors and below windows. And remember that the bigger the repeat, the less a part-used roll is worth: a half roll with a large repeat may contain no full drop at all. If your paper is a free match — plain textures and many grasscloth-style prints — leave the repeat at 0. That is what it is there for.

Measuring the room honestly

Perimeter

Measure the length and width at floor level, wall to wall. Do not assume the room is square, and do not assume opposite walls match — in older houses they routinely differ by a few inches; where they do, use the larger pair, so the perimeter errs on the generous side. Chimney breasts, alcoves and bays all add wall, and the tape is the only way to catch them: if the room is an awkward shape, run the tape right round the walls and enter half of that perimeter as the room length with the width set to 0 — the calculator's perimeter comes out exactly the same.

Ceiling height

Measure from the floor — or the top of the skirting, if the paper will stop there — to the ceiling, and measure in more than one place: ceilings slope and floors dip, so work from the tallest figure you find. Height is the least forgiving number in the whole calculation, because it is the drop length, height plus trim, that the roll length must divide into. A few extra inches can be the difference between three drops per roll and two; if your drop lands just over a clean division of the roll, expect the roll count to jump, and check whether the next roll size up works out cheaper.

Doors and windows

The calculator takes off a flat 3 ft (0.9 m) for every door and every window you enter — the width of wall that needs no full strips. That is a fair allowance for standard openings, with one honest warning: the paper above a door and below a window still has to come from somewhere. Those short pieces normally come out of the offcuts and part-drops the strip method has already rounded up, which is why the allowance works in practice. It does not stretch to a wall that is mostly glass, though: for openings much wider than 3 ft, count them at their real width — a 6 ft patio door is two doors for this purpose.

Buying advice: batches, spares and labels

• Buy every roll from the same batch or dye lot. Wallpaper is printed in runs, and colour varies slightly between them — a difference you cannot see roll to roll in the shop, but which shows plainly where two batches meet on a wall. The batch number is printed on the label; check that every roll carries the same one before you pay, and if you order online, state in the order notes that mixed batches are not acceptable.
• Order one extra roll. The calculator's figure is what the room needs, with trim and matching already allowed for. The extra roll is insurance against the strip you spoil, the wall that measures longer than you thought, and the repair you will want in three years' time — by which point your batch will be long gone. Keep it unopened, and most suppliers will take it back if the receipt and returns window allow.
• Keep the label. Photograph it, or peel it off and file it with your decorating notes. It carries the pattern number, batch, repeat and match type — everything needed to order an identical roll later, and everything the next person to paper the room will thank you for.
• Inspect before you cut. Unroll the first length of every roll and check for print faults, shading bands and damaged edges before any paste is mixed. A fault found before hanging is a straight exchange; the same fault found afterwards is an argument.

One last habit separates a calm job from a miserable one: plan the cutting before you paste anything. Number the strips in hanging order, work out which drops come from which roll, and only then start cutting. Ten minutes at the table is worth a roll on the wall.

Wallpaper guides

Want the thinking behind the numbers? These two guides walk through the strip method and the pattern repeat in full.

• How Many Rolls of Wallpaper Do I Need?
• Wallpaper Pattern Repeat — How It Changes Your Roll Count

Frequently asked questions