How to use the wallpaper calculator
- Choose metric or imperial units. You can switch at any time; your measurements are kept and converted.
- Add each wall you are papering with its width and height. In imperial mode, type feet and inches such as
8' 6"or decimal feet such as8.5. - Enter the roll width and length from the label, then pick the pattern match and enter the repeat if there is one.
- Adjust the trim allowances if your decorator uses different ones. 5 cm (2 in) at each end is a common starting point.
- Optionally add the price per roll, then print or save the plan to take shopping.
How the estimate is worked out
The calculation follows the way wallpaper is actually hung: in vertical strips (also called drops), each cut slightly longer than the wall is high.
- Strips per wall = wall width ÷ roll width, rounded up. The last strip on a wall is often narrower than the roll, but it still has to be cut at full height, so it counts as a whole strip.
- Cut length = wall height + top trim + bottom trim. With a straight-match pattern this is rounded up to a whole number of repeats, so that every strip starts at the same point in the design.
- Usable roll length = roll length, minus one repeat if you choose to set it aside for lining up the pattern at the start of the roll.
- Strips per roll = usable roll length ÷ cut length, rounded down. A leftover piece shorter than a full strip is not counted as a strip.
- Rolls: the calculator tries two simple cutting plans. In the first, each roll is cut into strips of one length only. In the second, strips of different lengths can share a roll, placing the longest strips first. It reports whichever plan needs fewer rolls. Neither plan is guaranteed to be the smallest possible number, and it only matters when your walls have different heights.
Worked example
A bedroom has two walls 4.2 m wide and two walls 3.5 m wide, all 2.4 m high. The paper is 53 cm wide and 10.05 m long, with a 64 cm straight-match repeat. The trim allowance is 5 cm at the top and 5 cm at the bottom.
- 4.2 ÷ 0.53 = 7.92, so each wide wall needs 8 strips. 3.5 ÷ 0.53 = 6.60, so each narrow wall needs 7 strips. Total: 8 + 7 + 8 + 7 = 30 strips.
- 2.40 + 0.05 + 0.05 = 2.50 m. 2.50 ÷ 0.64 = 3.91 repeats, rounded up to 4, so each strip is cut at 2.56 m.
- Setting aside one repeat leaves 10.05 − 0.64 = 9.41 m per roll. 9.41 ÷ 2.56 = 3.68, so each roll gives 3 strips.
- 30 ÷ 3 = 10 rolls. That is 100.5 m of paper, of which 76.8 m is used in full strips and 23.7 m is offcuts and alignment allowance.
Choose Try an example above (in metric) to see the same figures in the calculator.
Assumptions and limitations
- Rectangular walls, vertical strips. Sloped ceilings, stairwells, arches and ceilings are not modelled.
- Plain and straight-match papers only. Half-drop and other offset matches need extra length on alternate strips and are not calculated yet.
- Openings are not subtracted. Strips beside doors and windows are counted at full height.
- Offcuts are not reused for full-height strips. They are shown as unused material, although in practice they often cover the areas above doors and below windows.
- No allowance for mistakes or spare rolls. Add a roll if you want a margin.
- Check the manufacturer's hanging instructions. Some papers are hung with alternate strips reversed, or need a specific trim allowance.
Frequently asked questions
Why not just divide the wall area by the roll area?
Wallpaper is hung in full-height strips. A roll that is 10 m long cannot be used as one continuous strip if your walls are 2.5 m high: it gives a set number of whole strips, and the remainder is usually too short to use. Area-based estimates ignore that leftover and often come out a roll or two short, especially with a large pattern repeat.
Should I subtract doors and windows?
This calculator does not. Strips beside a door or window still need to be cut at full height before they are trimmed, and the short pieces above and below openings are usually cut from offcuts. Leaving openings in gives a safer figure. If a wall is mostly one large opening, such as patio doors, you can enter only the papered sections as separate walls.
What is a pattern repeat and where do I find it?
The vertical pattern repeat is the distance before the design starts again. It is printed on the roll label or product page, often as a number with a symbol showing the match type. Plain and "random match" papers have no repeat to allow for.
What is the difference between straight match and half-drop?
With a straight match, the design lines up horizontally across every strip, so each strip starts at the same point in the pattern. With a half-drop, every second strip is shifted down by half a repeat. Half-drop papers can need extra length per strip and are not calculated by this tool yet.
Should I buy a spare roll?
Many decorators buy one extra roll from the same batch (also called a lot or shade number) in case of mistakes or future repairs, because rolls from a different batch can differ slightly in colour. The calculator shows the minimum for its cutting plan; whether to add a spare is your choice.
Does the calculator work for ceilings, sloped walls or stairwells?
Not directly. It assumes rectangular walls papered with vertical strips. For a sloping wall, a cautious approach is to enter it at its tallest height. Stairwells, ceilings and walls with angled tops need a hand-drawn strip plan.
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