Wallpaper Calculator — How Many Rolls Do I Need?

We use the standard UK strip method used by Screwfix and Farrow & Ball: count the vertical strips (drops) needed to paper the whole room perimeter, work out the cut length of each drop (wall height plus a 100mm trim allowance, rounded up to the next whole pattern repeat), then see how many full drops you get from one roll.

The formula

Drops needed = Room perimeter ÷ Roll width (rounded up)

Cut length = round up (Ceiling height + 0.10m trim) to the next whole pattern repeat

Usable drops per roll = Roll length ÷ Cut length (rounded down; subtract one if it divides exactly)

Rolls needed = Drops needed ÷ Usable drops per roll × Wastage factor (rounded up)

For example, a room 4m × 3.5m with 2.4m ceilings, plain paper and standard rolls (10.05m × 0.53m): Perimeter = 15m. Drops needed = 15 ÷ 0.53 = 29 drops. Cut length = 2.4m + 0.10m = 2.50m. Drops per roll = 10.05 ÷ 2.50 = 4 drops. Rolls = 29 ÷ 4 = 8 rolls (rounded up). Add 10% wastage and round up if you want spare from the same batch.

Why the trim and pattern repeat matter

The 100mm trim (50mm top + 50mm bottom) lets you cut each drop square to the ceiling and skirting. With a patterned paper, every drop must be cut to the next whole multiple of the vertical repeat so the pattern lines up with the next strip — a longer repeat leaves a bigger offcut and gives fewer usable drops per roll. On a 2.4m wall and a standard 10.05m roll, plain paper or a stripe gives 4 drops per roll, and a small patterned repeat of around 180mm gives 3. Larger repeats push the cut length up further and reduce the count again, so the exact drops per roll depends on the precise repeat you enter. As a separate per-paper guide, Farrow & Ball quote roughly 3 drops per roll for their small patterns, 4 for stripes and 2 for their largest repeats on their own 10m rolls — always trust the figure the calculator returns for your specific repeat and ceiling height.

By default we paper the full perimeter (openings left in), because you still hang full-height drops beside doors and above and below windows. All results are rounded up because you cannot buy partial rolls, and we recommend an extra roll from the same batch for repairs and mistakes.