People type this into search every day: how much wallpaper do I need.
Floor area is the wrong input. Wallpaper is cut into vertical drops. You need the length of wall you will paper, the height of those drops, and the size of the roll.
The wallpaper quantity calculator estimates the roll count from those measurements. This page runs that estimate. It is not a substitute for the pattern repeat printed on the roll you are about to hang.
Drops, then rolls
The formula, in the order the tool runs it:
- Usable width = room perimeter minus the combined width of doors and windows. Openings are a length, in metres, not an area.
- Raw drops = usable width ÷ roll width.
- The tool multiplies by 1.1 and rounds up. That 10% is the allowance it uses for pattern matching and trimming.
- Drops per roll = roll length ÷ wall height, rounded down. The tool forces this to at least 1.
- Rolls to buy = drops ÷ drops per roll, rounded up.
Fig 1
Width becomes drops, then rolls
Height decides how many drops fit on a roll
Subtract opening widths, divide by the roll width, add 10%, then round up to whole rolls.
Farrow & Ball’s quantity guide describes the same family of measurement. Their standard roll is 10 m long and 53 cm wide, which is the calculator default of 0.53 m by 10 m. For a standard 2.4 m room they estimate four drops per roll on a stripe, three on a small repeat, and two on a large repeat. They also say to add one more roll for trimming and mistakes.
The calculator does not read a pattern repeat. floor(roll length ÷ height) matches their stripe case at 2.4 m, where 10 ÷ 2.4 = 4.17 and the floor is 4. A large repeat that only yields two drops per roll will need more rolls than this tool prints. Read the repeat on the label, then order.
The paint post subtracts doors and windows as square metres. This tool subtracts them as metres of width. A 2 m wide door is about 2 m in this field even if its area is over 4 m². The flooring post and the drywall post are area orders. Wallpaper is a drop order.
Example 1: the published defaults
- room perimeter: 16 m
- wall height: 2.5 m
- doors and windows width: 3 m
- roll width: 0.53 m
- roll length: 10 m
Usable width: 16 − 3 = 13 m. On a US display the card prints that as 42.7 ft.
Raw drops: 13 ÷ 0.53 = 24.5283.
With the 10%: 24.5283 × 1.1 = 26.9811, which rounds up to 27 drops.
Drops per roll: floor(10 ÷ 2.5) = 4.
Rolls: ceil(27 ÷ 4) = 7 rolls.
Calculator result
Wallpaper quantity
- Room perimeter
- 16 m
- Wall height
- 2.5 m
- Doors & windows width
- 3 m
- Roll width
- 0.53 m
- Roll length
- 10 m
7 rolls
wallpaper to buy
- Wall drops
- 27
- Drops per roll
- 4
- Usable wall width
- 42.7 ft
Four drops use 4 × 2.5 = 10 m, so a 10 m roll is full on this height, with nothing left for a fifth drop. 27 drops are 6 rolls of 4, plus a seventh roll that holds the last 3 drops. You still buy the seventh roll.
Skipping the 10% on this same room gives ceil(24.5283) = 25 drops, and ceil(25 ÷ 4) = 7 rolls. The allowance does not change the default order. Example 8 is a room where it does.
Example 2: a smaller room
- perimeter: 12 m
- height: 2.4 m
- openings: 1.8 m
- roll: 0.53 m by 10 m
Usable: 12 − 1.8 = 10.2 m (the card prints 33.5 ft).
Raw drops: 10.2 ÷ 0.53 = 19.2453. Times 1.1 = 21.1698, ceil = 22 drops.
Drops per roll: floor(10 ÷ 2.4) = 4.
Rolls: ceil(22 ÷ 4) = 6 rolls.
The height is Farrow & Ball’s “standard” 2.4 m, so four drops per roll matches their stripe estimate. A large repeat, on their guide, would be two drops per roll. The same 22 drops would then be ceil(22 ÷ 2) = 11 rolls. The tool will not make that change for you.
Example 3: a larger, slightly taller room
- perimeter: 22 m
- height: 2.7 m
- openings: 4 m
- roll: 0.53 m by 10 m
Usable: 22 − 4 = 18 m (59.1 ft on the card).
Raw drops: 18 ÷ 0.53 = 33.9623. Times 1.1 = 37.3585, ceil = 38 drops.
Drops per roll: floor(10 ÷ 2.7) = floor(3.703) = 3.
Rolls: ceil(38 ÷ 3) = 13 rolls.
The extra 0.2 m of height, against the 2.5 m default, costs a whole drop on every roll. 10 ÷ 2.5 was 4. 10 ÷ 2.7 is 3. That is why 38 drops become 13 rolls instead of ceil(38 ÷ 4) = 10 rolls.
Example 4: forgetting the doors
Hold the defaults and set openings to 0.
Usable: 16 m (52.5 ft).
Raw drops: 16 ÷ 0.53 = 30.1887. Times 1.1 = 33.2075, ceil = 34 drops.
Drops per roll: still 4.
Rolls: ceil(34 ÷ 4) = 9 rolls.
Calculator result
Wallpaper quantity
- Room perimeter
- 16 m
- Wall height
- 2.5 m
- Doors & windows width
- 0 m
- Roll width
- 0.53 m
- Roll length
- 10 m
9 rolls
wallpaper to buy
- Wall drops
- 34
- Drops per roll
- 4
- Usable wall width
- 52.5 ft
You would buy 2 rolls more than example 1. If the doors and windows really will be papered, 0 is the right opening width. If they will be skipped, type their combined width. A single 0.9 m door plus a 1.2 m window is 2.1 m, not “about one opening.”
Example 5: one centimetre of height that adds two rolls
Hold perimeter 16 m, openings 3 m, and the 0.53 m by 10 m roll.
- Height 2.40 m: drops per roll = floor(10 ÷ 2.40) = 4. Drops stay 27. Rolls: ceil(27 ÷ 4) = 7.
- Height 2.50 m (the default): still 4 per roll, still 7 rolls.
- Height 2.51 m: floor(10 ÷ 2.51) = floor(3.984) = 3. Rolls: ceil(27 ÷ 3) = 9.
Calculator result
Wallpaper quantity
- Room perimeter
- 16 m
- Wall height
- 2.51 m
- Doors & windows width
- 3 m
- Roll width
- 0.53 m
- Roll length
- 10 m
9 rolls
wallpaper to buy
- Wall drops
- 27
- Drops per roll
- 3
- Usable wall width
- 42.7 ft
The drop count did not change. The roll stopped fitting a fourth 2.51 m drop, because 4 × 2.51 = 10.04 m, and the roll is 10 m. Measure the height you will actually cut, including the trim the hanger needs. Farrow & Ball’s hanging note allows about 50 to 75 mm at the top and bottom for trimming. This calculator uses the height you type as the full drop. If the cut is longer than the wall, type the cut.
Example 6: a tall wall, and a roll that is too short
Same 16 m perimeter and 3 m of openings. The 27 drops do not change, because drops come from width.
- Height 3.4 m: floor(10 ÷ 3.4) = 2. Rolls: ceil(27 ÷ 2) = 14 rolls.
- Height 4.8 m: floor(10 ÷ 4.8) = 2. Still 14 rolls.
- Height 5.1 m: floor(10 ÷ 5.1) = 1. Rolls: 27 rolls, one drop on each roll.
- Height 11 m: floor(10 ÷ 11) = 0, then the tool forces the count to 1 drop per roll. The order is still 27 rolls.
An 11 m drop does not fit on a 10 m roll. The formula does not warn you. It will tell you to buy 27 rolls and assume you can cut one drop from each. If the drop is longer than the roll, you need a different product or a join the tool does not model. Check length against height before you trust a “1 drop per roll” result.
Fig 2 · 1/5
Rolls as the wall gets taller
16 m perimeter, 3 m of openings, a 0.53 m by 10 m roll.
Rolls
- Rolls
| Point | Rolls |
|---|---|
| 2.4 m | 7 |
| 2.5 m | 7 |
| 2.51 m | 9 |
| 3.4 m | 14 |
| 5.1 m | 27 |
At 2.4 m and 2.5 m the order is 7 rolls.
At 2.51 m it is 9. At 3.4 m it is 14. At 5.1 m it is 27.
Example 7: a double-width roll
Hold the default room. Change roll width from 0.53 m to 1.06 m. Length stays 10 m.
Raw drops: 13 ÷ 1.06 = 12.2642. Times 1.1 = 13.4906, ceil = 14 drops.
Drops per roll: still 4.
Rolls: ceil(14 ÷ 4) = 4 rolls.
Half the drops, and 4 rolls instead of 7. The order does not halve exactly, because both the 10% and the final round-up sit on whole drops. 27 ÷ 2 would have been 13.5 drops. The wider roll recalculates from the width, and 14 is the number that clears the 10% line.
Example 8: ignoring the 10%
On the default room, dropping the 10% still produced 7 rolls. Here are two rooms where the allowance changes the order. The calculator always applies the 10%. The “without” column is the same arithmetic with that step removed, so you can see the size of it.
Hallway: perimeter 18.4 m, height 2.5 m, openings 1.8 m, roll 0.53 m by 10 m.
Usable: 16.6 m (54.5 ft).
With the tool: 16.6 ÷ 0.53 × 1.1 = 34.4528, ceil = 35 drops. Drops per roll 4. Rolls: ceil(35 ÷ 4) = 9 rolls.
Without the 10%: ceil(16.6 ÷ 0.53) = ceil(31.3208) = 32 drops. ceil(32 ÷ 4) = 8 rolls.
One wall: perimeter 4.2 m, height 2.5 m, openings 0, same roll.
With the tool: 4.2 ÷ 0.53 × 1.1 = 8.717, ceil = 9 drops, 3 rolls. The card prints the usable width as 13.8 ft.
Without the 10%: ceil(7.9245) = 8 drops, ceil(8 ÷ 4) = 2 rolls.
Farrow & Ball’s own worked wall is a different check. Closet Stripe on a wall 2.5 m wide in a standard room is “about five drops, roughly two rolls” in their guide. Type perimeter 2.5 m, height 2.4 m, openings 0, roll 0.53 by 10:
2.5 ÷ 0.53 × 1.1 = 5.1887, ceil = 6 drops. floor(10 ÷ 2.4) = 4. ceil(6 ÷ 4) = 2 rolls.
Same order as their “roughly two rolls.” The drop count is 6 rather than about 5, because of the tool’s 10%. Their extra “add one more roll” would make it 3. This calculator will not add that roll on its own.
Example 9: typing the floor area into the perimeter box
A 5 m by 4 m room has floor area 5 × 4 = 20 m². Its perimeter is 2 × (5 + 4) = 18 m.
The room area calculator is the floor tool. Wallpaper wants the 18 m.
Paper the walls at 2.5 m high, with 3 m of openings, on a 0.53 m by 10 m roll.
Correct perimeter, 18 m:
Usable 15 m. 15 ÷ 0.53 × 1.1 = 31.132, ceil = 32 drops. Drops per roll 4. Rolls: ceil(32 ÷ 4) = 8 rolls.
Floor area typed as if it were the perimeter, 20 m:
Usable 17 m. 17 ÷ 0.53 × 1.1 = 35.283, ceil = 36 drops. Rolls: ceil(36 ÷ 4) = 9 rolls.
One extra roll, from using the floor number as a wall length.
The paint post’s sample room is 5 m by 3 m, perimeter 16 m, which is this wallpaper tool’s default perimeter. That paint example subtracts 5 m² of openings. If you type 5 into this tool’s opening field, you subtract 5 m of width:
Usable 16 − 5 = 11 m. 11 ÷ 0.53 × 1.1 = 22.830, ceil = 23 drops. Rolls: ceil(23 ÷ 4) = 6 rolls.
The default, with 3 m of opening width, is 7 rolls. Typing the paint area into the width field buys one roll too few on this room. Measure the widths.
Fig 3 · 1/5
Rolls for five wall runs
Same 0.53 m by 10 m roll, except the double-width case.
- Rolls
| Category | Rolls |
|---|---|
| Small | 6 |
| Default | 7 |
| Hall | 9 |
| Large | 13 |
| 1.06 m | 4 |
The small room is 6 rolls. The default is 7. The hallway is 9.
The large room is 13. A 1.06 m roll on the default room is 4.
Fig 4 · 1/3
What the openings do to the order
16 m perimeter, 2.5 m height, 0.53 m by 10 m roll.
Rolls
3 m openings
7 rolls
No openings
9 rolls
5 m typed
6 rolls
With 3 m of openings the order is 7 rolls.
With openings set to 0 it is 9 rolls. With 5 m typed in, it is 6.
The roll counts
| Example | Perimeter | Height | Openings | Roll | Drops | Per roll | Rolls |
|---|---|---|---|---|---|---|---|
| 1. Defaults | 16 m | 2.5 m | 3 m | 0.53 × 10 | 27 | 4 | 7 |
| 2. Smaller room | 12 m | 2.4 m | 1.8 m | 0.53 × 10 | 22 | 4 | 6 |
| 3. Larger room | 22 m | 2.7 m | 4 m | 0.53 × 10 | 38 | 3 | 13 |
| 4. No openings | 16 m | 2.5 m | 0 m | 0.53 × 10 | 34 | 4 | 9 |
| 5. Height 2.51 m | 16 m | 2.51 m | 3 m | 0.53 × 10 | 27 | 3 | 9 |
| 6. Height 3.4 m | 16 m | 3.4 m | 3 m | 0.53 × 10 | 27 | 2 | 14 |
| 6b. Height 5.1 m | 16 m | 5.1 m | 3 m | 0.53 × 10 | 27 | 1 | 27 |
| 7. Wider roll | 16 m | 2.5 m | 3 m | 1.06 × 10 | 14 | 4 | 4 |
| 8. Hallway | 18.4 m | 2.5 m | 1.8 m | 0.53 × 10 | 35 | 4 | 9 |
| 8b. One wall | 4.2 m | 2.5 m | 0 m | 0.53 × 10 | 9 | 4 | 3 |
| 9. True perimeter | 18 m | 2.5 m | 3 m | 0.53 × 10 | 32 | 4 | 8 |
| 9b. Floor area typed | 20 m | 2.5 m | 3 m | 0.53 × 10 | 36 | 4 | 9 |
| Stripe wall, 2.4 m high | 2.5 m | 2.4 m | 0 m | 0.53 × 10 | 6 | 4 | 2 |
A bedroom with perimeter 15 m (a 4 m by 3.5 m floor), height 2.4 m, and 2.1 m of openings lands on the same 7 rolls and 27 drops as the default, with 4 drops per roll. The usable width is 12.9 m, which the card prints as 42.3 ft. Same order, different room.
Open the wallpaper calculator with the roll width and length from the label in your hand. If the pattern repeat is large, ask the maker how many drops that repeat yields, and raise the order when their number is below the tool’s drops per roll.