RoomRoll Calculator
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Five Wallpaper Calculations, Worked Step by Step

Every figure on this page was produced by the calculator on this site, with the arithmetic written out so you can follow it and check your own room.

Why we publish the arithmetic

Most wallpaper calculators show a single number and no working. That makes it impossible to tell whether the estimate suits your room or whether it has quietly assumed something that is not true of your walls. The five examples below are run through the same formula as our wallpaper roll calculator, and each step is shown with its result, so you can see exactly where a number comes from and at which point your own room would diverge.

All five use a standard European roll of 0.53 m by 10 m unless stated otherwise. Real European rolls are usually 10.05 m long; in these particular examples the extra five centimetres does not change the final roll count, but you should still enter the exact length printed on your own product label rather than a rounded figure.

Plan view and wall elevation of a rectangular roomA rectangle seen from above with length 4.2 metres and width 3.6 metres, and a wall seen from the front with a height of 2.4 metres divided into vertical strips 0.53 metres wide. Plan view (from above) length 4.2 m width 3.6 m perimeter =2 x (4.2 + 3.6) = 15.6 m Wall elevation (from the front) height 2.4 m 0.53 m one strip per 0.53 m of perimeter
The calculator works from the room perimeter and the wall height, then checks how many full-height strips fit across that perimeter. The shaded band is a single strip at standard European roll width.

Example 1: a standard double bedroom

4.2 x 3.6 m, 2.4 m ceiling

Eight rolls

A rectangular bedroom with one door, a plain wallpaper and the default 15% allowance.

Room length4.2 m
Room width3.6 m
Wall height2.4 m
Roll size0.53 x 10 m
Allowance15%
Openings1 door
  1. Perimeter of the room: 2 x (4.2 + 3.6) = 15.6 m
  2. Gross wall area: 15.6 x 2.4 = 37.44 m²
  3. Rough allowance for one door: 37.44 - 1.6 = 35.84 m²
  4. Add the 15% waste allowance: 35.84 x 1.15 = 41.22 m²
  5. Nominal area of one roll: 0.53 x 10 = 5.30 m²
  6. Area estimate: 41.22 / 5.30 = 7.78, rounded up to 8 rolls
  7. Strip check — strips needed: 15.6 / 0.53 = 29.4, rounded up to 30 strips
  8. Full-height drops in one roll: 10 / 2.4 = 4.17, rounded down to 4 drops
  9. Strip estimate: 30 / 4 = 7.5, rounded up to 8 rolls
Result: 8 rolls. Both methods agree, which is the comfortable case. The eight rolls carry 42.4 m² of nominal paper for 35.84 m² of wall, so there is roughly 6.5 m² of slack for trimming and mistakes.

Example 2: a large living room with a 2.7 m ceiling

5.5 x 4.0 m, 2.7 m ceiling

Twelve rolls

The same roll and allowance, but a taller ceiling and no deduction for openings.

Room length5.5 m
Room width4.0 m
Wall height2.7 m
Roll size0.53 x 10 m
Allowance15%
Openingsnot deducted
  1. Perimeter: 2 x (5.5 + 4.0) = 19.0 m
  2. Gross wall area: 19.0 x 2.7 = 51.30 m²
  3. With the 15% allowance: 51.30 x 1.15 = 58.99 m²
  4. Area estimate: 58.99 / 5.30 = 11.13, rounded up to 12 rolls
  5. Strips needed: 19.0 / 0.53 = 35.8, rounded up to 36 strips
  6. Drops per roll: 10 / 2.7 = 3.70, rounded down to 3 drops
  7. Strip estimate: 36 / 3 = 12, exactly 12 rolls
Result: 12 rolls. Notice what the ceiling height did. At 2.4 m this roll yields four drops; at 2.7 m it yields three, and 1.9 m of every roll becomes an offcut too short to hang. The wall area grew by 37% compared with Example 1, but the roll count grew by 50%.
How many full-height drops come out of one 10 metre rollA 10 metre roll divided into four usable drops of 2.4 metres each, leaving a 0.4 metre offcut, compared with a 2.7 metre wall where only three drops fit and 1.9 metres is left over. Wall height 2.4 m — four drops fit 2.4 m2.4 m2.4 m2.4 m 0.4 m Wall height 2.7 m — only three drops fit 2.7 m2.7 m2.7 m 1.9 m unusable
Drops per roll is a whole number, so a taller wall can waste a large part of every roll. At 2.4 m a 10 m roll gives four drops; at 2.7 m it gives three, and almost two metres of each roll is left as an offcut too short to hang.

Example 3: a narrow stairwell, where the two methods disagree

3.0 x 1.2 m, 3.6 m height

Eight rolls, not seven

This is the example that shows why an area-only calculation can leave you short.

Room length3.0 m
Room width1.2 m
Wall height3.6 m
Roll size0.53 x 10 m
Allowance20%
Openingsnot deducted
  1. Perimeter: 2 x (3.0 + 1.2) = 8.4 m
  2. Gross wall area: 8.4 x 3.6 = 30.24 m²
  3. With a 20% allowance: 30.24 x 1.20 = 36.29 m²
  4. Area estimate: 36.29 / 5.30 = 6.85, rounded up to 7 rolls
  5. Strips needed: 8.4 / 0.53 = 15.8, rounded up to 16 strips
  6. Drops per roll: 10 / 3.6 = 2.78, rounded down to 2 drops
  7. Strip estimate: 16 / 2 = 8, exactly 8 rolls
Result: 8 rolls. The two methods disagree by a whole roll, and the calculator reports the higher figure. An area-only estimate would have told you seven. Each roll here produces two usable 3.6 m drops and wastes 2.8 m, so 28% of every roll is thrown away before any pattern matching is considered. Tall, narrow spaces are where nominal square metres are least trustworthy.

Example 4: a small cloakroom

2.1 x 1.5 m, 2.4 m ceiling

Four rolls

Small rooms round up harshly, because a roll is indivisible.

Room length2.1 m
Room width1.5 m
Wall height2.4 m
Roll size0.53 x 10 m
Allowance10%
Openings1 door
  1. Perimeter: 2 x (2.1 + 1.5) = 7.2 m
  2. Gross wall area: 7.2 x 2.4 = 17.28 m²
  3. Less a rough door allowance: 17.28 - 1.6 = 15.68 m²
  4. With a 10% allowance: 15.68 x 1.10 = 17.25 m²
  5. Area estimate: 17.25 / 5.30 = 3.25, rounded up to 4 rolls
  6. Strips needed: 7.2 / 0.53 = 13.6, rounded up to 14 strips
  7. Drops per roll: 4, so strip estimate 14 / 4 = 3.5, rounded up to 4 rolls
Result: 4 rolls. Four rolls hold 21.2 m² of nominal paper for 15.68 m² of wall — about 35% more than the bare wall area. In a room this small, rounding up dominates the waste percentage you chose, so the difference between a 10% and a 15% allowance often changes nothing at all.

Example 5: a room measured in feet, with a US roll

12 x 14 ft, 8 ft ceiling

Nine rolls

Mixed units, converted to metres internally before any calculation happens.

Room length12 ft
Room width14 ft
Wall height8 ft
Roll width20.5 in
Roll length33 ft
Allowance15%
  1. Everything converts to metres first: 12 ft = 3.66 m, 14 ft = 4.27 m, 8 ft = 2.44 m, 20.5 in = 0.52 m, 33 ft = 10.06 m
  2. Perimeter: 2 x (3.66 + 4.27) = 15.85 m
  3. Gross wall area: 15.85 x 2.44 = 38.65 m²
  4. With the 15% allowance: 38.65 x 1.15 = 44.44 m²
  5. Nominal roll area: 0.52 x 10.06 = 5.24 m²
  6. Area estimate: 44.44 / 5.24 = 8.48, rounded up to 9 rolls
  7. Strips needed: 15.85 / 0.52 = 30.4, rounded up to 31 strips
  8. Drops per roll: 10.06 / 2.44 = 4.12, rounded down to 4; strip estimate 31 / 4 = 7.75, rounded up to 8 rolls
Result: 9 rolls. Here the area estimate is the higher of the two, so it wins. One caution specific to the United States market: wallpaper is frequently priced per single roll but packaged and sold only in double rolls. Nine single rolls means buying five doubles. Our roll sizes and usable coverage page explains that difference.

What the waste allowance actually changes

The allowance dropdown is the control people adjust most, usually expecting a proportional effect. Because the result is rounded up to whole rolls, its influence is lumpy. Using the bedroom from Example 1 and changing only the allowance:

AllowanceArea after allowanceArea estimateStrip estimateRolls reported
10%39.42 m²888
15%41.22 m²888
20%43.01 m²989

Moving from 10% to 15% changes nothing in this room, while moving to 20% adds a whole roll. That is not a flaw in the arithmetic; it reflects the fact that you cannot buy four fifths of a roll. It also means a generous allowance is sometimes free and sometimes expensive, depending on where your room sits relative to the rounding boundary. It is worth trying both values before you order.

What these examples cannot tell you

Every room above is a plain rectangle with square corners, a level floor and a uniform ceiling height, and every wallpaper is treated as having no pattern repeat. Real projects break those assumptions regularly, and in ways that only add material:

  • A pattern repeat forces each strip to start at a particular point in the design, which can add the length of one repeat to every drop. A 64 cm repeat on a 2.4 m wall can push a four-drop roll down to three.
  • Sloped ceilings, stairwells, chimney breasts and alcoves need a wall-by-wall plan rather than a perimeter figure.
  • Rooms are rarely exactly rectangular. Measuring each wall separately and adding the widths gives a better perimeter than measuring two sides and doubling.
  • The door allowance used above is a flat 1.6 m² placeholder, not a measurement of your door. Windows are not deducted at all.
  • Dye lots vary between production batches, so ordering a single extra roll later may not match what is already on the wall.

For those reasons we would rather the calculator over-order slightly than leave you one strip short halfway up a wall. If a result looks higher than you expected, Example 3 is usually the reason why.

Check your own room

Open the calculator, enter your measurements and compare the figures it reports with the steps above; the labels match. If a number does not look right, the method page defines each term, the planning guide covers measuring and pattern repeat, and the FAQ answers the questions we are asked most. When the result matters financially, take your measurements and the exact product label to your supplier or installer and ask them to confirm the quantity before you order.

Written and checked by the publisher of RoomRoll Calculator. Last reviewed 18 October 2026. The figures on this page were calculated with the same formula as the site’s calculator and checked against it. If you find an error, email gamejadoo100@gmail.com and we will correct it and note the change here.