How to use the wallpaper calculator
- Measure each wall separately, including the width occupied by doors and windows. Add a wall for each separate rectangular face. Use the greatest finished height if the walls are nearly equal; calculate substantially different heights separately. This tool is for homeowners comparing roll requirements before placing an order.
- Choose centimetres or inches for all measurements. A 10.05 m roll is 1,005 cm; a 33 ft roll is 396 in. Enter the physical roll length and usable width printed on the product, rather than the advertised coverage area or a price described as a single roll.
- Enter the combined trimming allowance for the top and bottom of each strip. The starting example uses 10 cm in total, not 10 cm at each end. Confirm the allowance with the product instructions and the actual ceiling and skirting levels.
- Select free, straight or offset half-drop matching. Patterned modes need the full vertical repeat from the label. Add optional whole spare rolls, press Calculate rolls and review the intermediate values. Copy estimate puts the current inputs, results and assumptions into plain text for your notes.
How the strip and roll calculation works
A drop is one full-height vertical strip. Each wall width is divided by the roll width and rounded up separately. A narrow final strip still uses a full drop in this estimate. The per-wall counts are then added; leftover width from one wall is not automatically carried around a corner.
Free-match cut length is wall height plus total trim. Straight-match length is that minimum rounded up to a whole vertical repeat. For half-drop, the length is the smallest number of whole repeats plus one half-repeat that reaches the minimum. Successive cuts therefore begin half a repeat apart, allowing an A/B sequence. Other offsets, reversed alternate strips and special multi-panel designs are outside this calculation.
A fresh roll may begin at an arbitrary point in the design. For either patterned mode, the estimate reserves one full repeat at each roll start before dividing the remaining length by the cut length and rounding down. This makes room to align the next required pattern phase. It can overestimate compared with a measured, optimized cutting plan, especially when the factory starts are already aligned.
Divide total drops by complete drops per roll and round up to obtain base rolls, then add the selected extra rolls. The tail figure describes the remainder after cutting a full allocation from one roll. It excludes the starting reserve and does not include unused drop positions in the last roll; it is not a promise of reusable material.
Two worked examples
Free match: one 400 cm wide wall, height 240 cm, roll 53 × 1,005 cm, total trim 10 cm and zero extra rolls. The wall needs ceil(400 ÷ 53) = 8 drops. Cut length is 250 cm; floor(1,005 ÷ 250) = 4 fit per roll. The result is 2 rolls, with a 5 cm tail on each fully cut roll.
Pattern comparison: keep those dimensions and enter a 64 cm repeat. Straight match gives 256 cm cuts; after a 64 cm starting reserve, 3 fit per roll, so 8 drops need 3 rolls. Half-drop gives 288 cm cuts and also 3 rolls. Adding one extra roll changes either total to 4. Equal roll counts do not mean equal cutting waste.
Planning, limits and common mistakes
Use the calculator to compare plain and patterned papers, assess a feature wall or prepare a shopping note. Do not reduce the roll length to a marketing “usable area” first: the calculation already accounts for strip cutting. Include openings because pieces above and below them may still need matching. For very large openings, alcoves, sloping ceilings or multiple wall heights, have the actual strip layout checked before ordering. Changes to an input clear the previous result so it cannot be mistaken for a current estimate.
Frequently asked questions
Can I subtract doors and windows?
This tool deliberately makes no area deduction. A door is usually shorter than the wall, and the strip above it still needs paper. A precise reduction needs opening positions and a cutting plan, which are not modeled here.
Does every offset pattern use half a repeat?
No. Select offset only when the label specifies half-drop, such as a 64/32 cm repeat/offset. A different offset or an A/B product supplied in separate panels needs the manufacturer’s own instructions.
Why does a tiny height change add a roll?
Only complete drops count. Crossing a repeat boundary may lengthen every cut enough to reduce roll capacity. Recheck measurements rather than shortening trim solely to reach a cheaper answer.
Are spare rolls already included?
Only the number shown in Extra whole rolls is added. The default is zero. This is separate from trim, pattern alignment and roll rounding. Confirm matching batch numbers and any repair allowance with your supplier.
Will my inputs be saved?
The calculation runs in your browser, without an account or input upload. Copy the estimate before reloading or changing language; there is no saved project history. Dimensions use a decimal point or comma, without grouping separators.