How this calculation works
Count full-width drops for each wall separately. Adjust every drop to a whole pattern repeat when one is entered. Only whole adjusted drops fit in each usable roll. Add entered spare drops and round up the roll count.
Cut length = ceil((height + trim)/repeat) × repeat; rolls = ceil(required drops / floor(usable roll length/cut length))A worked example
Wall widths 4,3,4,3 m at 0.53 m per strip need 28 drops. Height plus trim is 2.5 m, rounded to 2.56 m at a 0.64 m repeat. Three drops fit a 10.05 m usable roll, so 10 rolls are needed.
Good to know
A geometric material-planning estimate from the entered measurements. Check actual product dimensions and the project layout. No structural suitability, installation specification, local requirements, labor, tax or pricing is determined. Decimal input lists allow up to 6 places and at most 100 entries/rows, each no greater than 1,000,000. Only no-repeat or straight-match vertical drops. No half-drop matching, openings deduction or cross-wall partial-strip reuse. Usable roll length assumes leading alignment waste is already removed.
Reference: Sherwin-Williams: wallpaper roll dimensions and pattern repeat (opens in a new tab) ↗
Area alone can overstate the usable yield of a roll
Wallpaper is often cut as full-height drops. A roll can have enough total area on paper yet fail to provide another complete drop after pattern matching and trimming. Counting whole drops exposes that difference.
For a wall height of 2.4 m and total trim allowance of 0.1 m, the initial cut length is 2.5 m. A straight-match repeat of 0.64 m rounds that to four repeats, or 2.56 m. Only three such drops fit into 10.05 m of usable roll length.
Wall widths are rounded separately to whole wallpaper widths. A 4 m wall at 0.53 m per drop needs eight drops. This model does not assume that a narrow leftover strip from one wall can be reused successfully at another corner.
Use the dimensions of the actual product being purchased
Enter usable roll length after any leading alignment loss. If a product’s first pattern position needs trimming, that length is unavailable for full drops. A single-roll or double-roll sales label is not a universal physical dimension.
Door and window openings are not deducted because this is a conservative full-height-drop model. Openings can permit reuse in a real layout, but their area alone does not establish how partial pieces will match the pattern. Half-drop matching is also outside this model.
Paint quantity instead uses coverage per area and coat count; it cannot be substituted for a full-drop wallpaper calculation. Both tasks require measured wall dimensions, but their material-yield constraints are different.
A few questions, answered
Does this support half-drop patterns?
No. Use it for no-repeat or straight-match vertical drops. A half-drop pattern needs an appropriate alternating layout.
What does trim mean here?
The total extra length per drop for top and bottom trimming combined, before pattern-repeat rounding.
Why can adding a small width require a whole extra roll?
Widths and roll yields are rounded to whole drops. Crossing a drop-count boundary can increase the whole-roll count.