Wallpaper roll calculator

Wallpaper rolls come in a standard size, but the number of usable lengths you actually get from one depends heavily on pattern repeat — and that's where estimates most often go wrong, especially on a bold or large-scale pattern.

Drops, not square metres

Wallpaper isn't bought by area the way paint is — it's bought by the drop, a single length cut to run from skirting (or dado) to ceiling. Every drop cut from a roll has to be the same length, because the pattern has to line up as you move around the room. That's why coverage doesn't scale simply from wall area the way it does with paint; it scales from how many equal-length drops a roll actually yields.

Why pattern repeat costs extra rolls

Every drop has to be a whole number of pattern repeats long, so it lines up with the drop next to it — which means the usable drop length rounds up to the next repeat, and whatever's left over is waste. A bigger repeat means more rounding, more waste per drop, fewer usable drops per roll, and ultimately more rolls needed to cover the same wall than a plain paper with no repeat to match at all.

A worked example

A 2.4m wall height plus a 10cm trim allowance gives a 2.5m drop. On plain paper, a standard 10.05m roll yields four drops. With a 64cm pattern repeat, each drop rounds up to 2.56m, and the same roll only yields three. For a 12m wall run needing 23 drops at a standard 0.53m roll width, that's the difference between 6 rolls for plain paper and 8 rolls for the patterned version — two extra rolls, from the repeat alone.

What this isn't

This assumes a straight (not random) pattern match and doesn't account for chimney breasts, alcoves, large openings, or the extra care needed around them. Always check the roll's own repeat and match type against the label, and buy every roll from the same batch — dye lots vary enough between batches to show as a visible colour shift once it's on the wall.