Wallpaper Calculator
Lay your walls out on the roll and count the drops, the way an installer does, instead of dividing area by a coverage figure.
Sheet 1 of 9
Counts drops the way an installer counts them, then prints the area ÷ coverage figure beside it so you can watch the two disagree on your own room.
Priced by the single roll, sold by the double. Pattern match and waste are set on the ticket, not assumed.
Order
9rolls
22 drops × 1.10 waste = 25 → ÷ 3 per roll = 8.33 → 9 rolls
- Drops needed
- 22
- Drops per roll
- 3
- Cut length per drop
- 8 ft 9 in
- Wall area
- 352 sq ft
- Paper in the order
- 547 sq ft
- Left on the last roll
- 24 ft 3 in
- Area ÷ coverage check under-orders by 2 on this repeat
- 7 rolls
Your walls, in drops
What this calculator does differently
Most wallpaper calculators and estimators divide your wall area by a fixed number of square feet per roll and hand back a count. That works for plain paper on a simple wall and fails quietly the moment a pattern repeat appears, because a roll does not yield area. It yields drops: whole vertical strips cut to the height of the wall plus whatever the pattern forces you to round up.
This sheet counts the way an installer counts. It works out how many drops each wall needs, how long each drop has to be cut, how many of those cuts one roll gives you, and then how many rolls cover the drops with a margin for error. The roll drawing above is not an illustration of that process. It is the process, redrawn on every keystroke. Add as many walls as the room has, up to twelve, in feet and inches: the sheet works wall by wall, so it serves a single wall, a whole room or several rooms at once. It runs in your browser, with no app to install.
The paper type does not change any of this. Vinyl, non-woven, paper-backed and grasscloth all hang in vertical drops, so the amount of wallpaper you need comes from the same arithmetic. What changes it is the roll size and the repeat.
Two habits of the US trade are stated on the ticket because they change the number you take to the shop: paper is priced by the single roll and packaged as a double, and openings are usually left in the estimate on patterned paper. Both are explained in the guides, and neither is decided for you.
Wallpaper terms the calculator uses
- Roll width
- The width of paper on the roll, from the label. US rolls are usually 20.5 in or 27 in wide; European rolls are 53 cm, about 20.9 in.
- Roll length
- The length of paper on one roll. Copy it from the label and check whether the label means a single or a double roll.
- Drop
- One full-height vertical strip of paper. Every wall needs a whole number of drops, however narrow the last one is.
- Cut length
- The length each drop is cut to: wall height plus trim, rounded up to fit the pattern.
- Pattern repeat
- The vertical distance before the design starts again, printed on the label. A repeat of 0 means plain or random paper.
- Match
- How the pattern lines up from one drop to the next: straight, half-drop or random.
- Trim
- Extra length at the top and bottom of each drop so it can be cut clean at the ceiling and the skirting. The calculator allows 4 in per drop.
- Waste allowance
- A margin for spoiled drops, mistakes and awkward corners, added to the drop count as a percentage.
How the wallpaper calculator works
Measure every wall you will paper
Width along the floor, height floor to ceiling, in feet and inches. Add each wall on the ticket and note the size of every door and window. The sheet lists the walls A, B, C so the drawing and the readout agree.
Copy the roll off the label
Roll width, roll length, and the vertical repeat. Labels vary, so the defaults are only a starting point. If the label gives metres and centimetres, use the metric sheet.
Pick the match type
Random needs no alignment. Straight repeats level across drops. Half-drop steps alternate drops down by half a repeat. The match sets how much each cut has to be rounded up.
Set the waste allowance
10% is the trade habit. Go to 15–20% for a large repeat, a half-drop, a complicated room, or a first attempt. The waste guide has the reasoning.
Decide about doors and windows
Leave them in unless the paper is plain and the openings are large. The box on the ticket deducts them in whole drops and tells you how many it saved.
Read the roll, then the number
The drawing shows how many drops one roll yields and where it runs out. The rack under it shows every roll in the order. The count is rounded up, always.
The step-by-step guide walks the same six steps through a full room with the arithmetic written out.
How to measure walls, doors and windows
Measure each wall on its own: width along the floor and height from floor to ceiling, in feet and inches. Measure the height in two or three places and use the tallest, because floors and ceilings are rarely level. Each wall gets its own row, so one wall, a whole room or several rooms all work the same way, and there is no need to convert to square feet first.
For doors and windows, measure the width and height of each opening, frame included. Tick the box on the ticket only if you want them deducted: the calculator removes them in whole drops, never as a slice of area, and shows how many drops that saves.
On patterned paper it is usually safer to leave small doors and windows in, because the paper around them still has to match and the offcuts are rarely usable. The doors and windows guide explains when deducting is worth it. If your roll labels are in metres and centimetres, as in the UK, Australia and New Zealand, use the metric sheet instead.
The formula, in two parts
Strip method (what to order from)
- Drops per wall
- ceil( wall width ÷ roll width )
- Cut length
- wall height + trim, rounded up to a whole repeat (half-drop: + ½ repeat)
- Drops per roll
- floor( roll length ÷ cut length )
- Rolls
- ceil( drops × (1 + waste) ÷ drops per roll )
Waste is added to the drop count before dividing, because waste arrives as a spoiled drop, not as a spoiled roll.
Area ÷ coverage (a check, not an order)
- Rolls
- ceil( wall area × (1 + waste) ÷ (roll width × roll length) )
This is the arithmetic behind the fixed "56 sq ft per roll" some retailers use. It ignores the cut length, so on a 21 in repeat with 8 ft walls it reads low. The readout shows it beside the strip count so you can see the gap on your own room rather than take it on trust.
Straight, half-drop and random match
Straight match
The design lines up level across every drop. Each cut is rounded up to a whole number of repeats, so a larger repeat loses more paper per drop.
Half-drop match
Every second drop is shifted down by half a repeat, so the pattern runs diagonally across the wall. Each cut needs an extra half repeat, which usually means fewer drops per roll.
Random match (no repeat)
Stripes, textures and plain paper line up anywhere. There is nothing to round to, so each cut is wall height plus trim. Set the repeat to 0 if the label gives none.
The match type is printed on the label, usually as a symbol. The pattern repeat guide shows how each one changes the order.
Roll sizes you will see on labels
| Roll | Width | Length | Paper area | Drops at 8 ft, no repeat |
|---|---|---|---|---|
| US single roll | 20.5 in | 16.5 ft | ≈ 28 sq ft | 1 |
| US double roll | 20.5 in | 33 ft | ≈ 56 sq ft | 3 |
| US double roll (wide) | 27 in | 27 ft | ≈ 61 sq ft | 3 |
| European roll | 53 cm (20.9 in) | 10 m (32.8 ft) | ≈ 57 sq ft · 5.3 m² | 3 |
| European roll (narrow) | 52 cm (20.5 in) | 10 m (32.8 ft) | ≈ 56 sq ft · 5.2 m² | 3 |
"Drops at 8 ft" assumes an 8 ft wall plus 4 in of trim and no pattern rounding. Add a 21 in straight repeat and the 27 ft roll still yields 3, while a 16.5 ft single yields 1. For metric rolls and metre inputs use the metric sheet. For common room sizes see the room-size chart.
A worked room
The ticket opens on a 10 × 12 ft bedroom with 8 ft ceilings: two walls of 10 ft and two of 12 ft. The roll is a 27 in × 27 ft double with a straight match on a 21 in repeat, and the waste is 10%.
- Drops: 10 ft is 120 in ÷ 27 = 4.4 → 5. 12 ft is 144 ÷ 27 = 5.3 → 6. Two of each: 22 drops.
- Cut length: 96 in + 4 in trim = 100 in, rounded up to a whole 21 in repeat → 105 in (8 ft 9 in).
- Drops per roll: 27 ft is 324 in ÷ 105 = 3.09 → 3, with 9 in left on each roll.
- Waste: 22 × 1.10 = 24.2 → 25 drops.
- Rolls: 25 ÷ 3 = 8.33 → 9 double rolls.
The area method says 352 sq ft × 1.10 ÷ 60.75 sq ft = 6.4 → 7 rolls. Order 7 and you run out two rolls short, at the point where the dye lot has probably sold out.
Change one thing
- Random match, no repeat9 rolls
- Half-drop on the same 21 in13 rolls
- Waste 15% instead of 10%9 rolls
- Deduct one door and one window8 rolls
- Same walls, 20.5 in × 33 ft roll11 rolls
Half-drop hurts most because 105 in becomes 115.5 in and only two drops fit on a 27 ft roll. Random match still needs 9 here because 22 drops at three per roll is already 8 rolls before waste. Every figure comes from the ticket above; change the inputs to reproduce them.
Common wallpaper calculation mistakes
Dividing wall area by roll coverage
Area ÷ coverage ignores the cut length, so it reads low as soon as the paper has a repeat. Count drops instead.
Forgetting trim
Every drop needs a few inches extra at the top and bottom. Without it, each cut comes out short.
Ignoring the pattern repeat
A large repeat or a half-drop can cost a whole drop per roll. Copy the repeat from the label rather than guessing.
Mixing dye lots
Rolls from different print runs can differ in tone. Buy the full count at once and check the lot numbers match.
Rounding down
A roll that runs out 10 in before the end of the last drop does not cover that drop. Always round rolls up and keep the waste allowance.
The other eight sheets
- 2Accent Wall CalculatorSingle-wall strip method
- 3Wallpaper Mural CalculatorPanel grid
- 4Peel and Stick Wallpaper CalculatorStrip method with peel presets
- 5Wallpaper by the Yard CalculatorLinear yardage
- 6Ceiling Wallpaper CalculatorPlane strip method
- 7European Wallpaper Roll CalculatorMetric strip method
- 8Wall Panel CalculatorPanel grid with gaps
- 9Wainscoting CalculatorLinear run and height
Nothing on this site is for sale.
Questions people ask
How many rolls of wallpaper do I need?
Count drops, not square feet. For each wall, divide its width by the roll width and round up: that is the number of drops. Work out the cut length (wall height plus about 4 in of trim, rounded up to the pattern repeat if the paper has a match). Divide the roll length by the cut length and round down: that is drops per roll. Add your waste allowance to the drop count, divide by drops per roll, and round up. The calculator above does exactly this and draws the cuts on the roll so you can check it.
How much wallpaper do I need?
Enough rolls to give you every drop, plus a margin. Measure each wall's width and height, take the roll width, roll length, and vertical repeat from the label, and enter them above. The answer comes back as rolls, with the total drops and the paper area shown underneath. If you were quoted a figure in square feet, the readout shows the area too, but order by rolls.
How do I calculate how much wallpaper I need?
Six steps. Measure wall widths and heights. Read the roll width, roll length, and repeat off the label. Decide the match type (random, straight, or half-drop). Divide wall width by roll width for drops. Divide roll length by cut length for drops per roll. Divide drops (with waste) by drops per roll and round up. The step-by-step guide walks through a full room.
How much does a wallpaper roll cover?
Multiply roll width by roll length. A US double roll of 27 in × 27 ft covers about 60 sq ft of paper. A 20.5 in × 33 ft double roll covers about 56 sq ft, and a European 53 cm × 10 m roll about 57 sq ft (5.3 m²). Usable coverage is less than that once each drop is cut to length and matched, which is why this calculator counts drops per roll instead of dividing area by coverage.
How many double rolls of wallpaper do I need?
It depends on which roll you described. In the US, wallpaper is priced by the single roll but almost always packaged and sold as a double roll. If you entered the double roll's length from the label, the count above is already double rolls. If you entered a single-roll length, buy half as many double rolls, rounded up. Set the packaging switch on the ticket and the readout translates for you. The single vs double roll guide explains the pricing habit.
How do I calculate how much wallpaper I need with a pattern?
The pattern changes the cut length, not the number of drops. With a straight match, each drop has to start at the same point in the pattern, so round the cut length up to a whole number of repeats. With a half-drop match, alternate drops shift by half a repeat, so allow an extra half repeat on top. A longer cut means fewer drops per roll, which is where patterned paper costs you. Choose the match type above and the hatched allowance on each drop shows the extra length. The pattern repeat guide has the detail.
How much wallpaper do I need for one wall?
Use the accent wall calculator, which is built for a single wall. The math is the same strip method, but the page is set up for one width, one height, and one optional door or window, so you are not adding and removing walls.
Should I deduct doors and windows from a wallpaper estimate?
Often not, and never silently. A drop that passes a door still has to run full height above it and match its neighbours, so on patterned paper the saving is smaller than the opening's area suggests. On plain or random-match paper with large openings, deducting is reasonable. The calculator leaves openings out unless you tick the box, and shows how many drops it saved when you do. The doors and windows guide lays out when each choice is safer.
How much wallpaper do I need for a 10x12 room?
With 8 ft ceilings, a 27 in × 27 ft double roll, a straight match on a 21 in repeat, and 10% waste, a 10 × 12 room needs 22 drops and 9 rolls. Change the repeat to none and it drops to 7. The room-size chart lists common rooms under stated assumptions, and the calculator above takes your exact walls.
What is the wallpaper calculation formula?
Drops = Σ ceil(wall width ÷ roll width). Cut length = wall height + trim, rounded up to the repeat (plus half a repeat for half-drop). Drops per roll = floor(roll length ÷ cut length). Rolls = ceil(drops × (1 + waste) ÷ drops per roll). The area method, wall area ÷ roll coverage, is shown as a cross-check because it under-orders whenever the repeat is large. The how-to guide works the formula on a real room.