Decorators don't estimate wallpaper by area — they count drops, the ceiling-to-floor strips that go around the room. Two quick divisions do the job: how many drops fit around the walls (perimeter ÷ roll width) and how many drops you can cut from one roll (roll length ÷ drop length). Divide one by the other and round up for the roll count. This method is more reliable than area maths because each strip has a fixed length and a fixed amount of unavoidable trim — and it naturally handles pattern repeats, which waste paper.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the standard decorator's drop (strip) estimating method.
The wallpaper equations
The drop length is the ceiling height plus any pattern repeat, since each strip must be cut a little long to match its neighbour. Dividing the roll length by that gives whole drops per roll (round down — a part-drop is useless). The perimeter divided by the roll width gives how many drops go around the room (round up). Rolls is the total drops divided by drops per roll, rounded up to whole rolls.
Worked example — papering a room
Scenario: A room with an 18 m wall perimeter and 2.4 m ceilings, using a plain 10 m × 0.53 m roll with no pattern repeat.
You need 9 rolls. Raise the ceiling to 2.7 m and each roll yields only 3 drops (10 ÷ 2.7 = 3.7, rounded down), pushing the count to 12 rolls — taller walls cost disproportionately because that lost part-drop is wasted on every roll. Add a 0.3 m pattern repeat at 2.4 m ceilings and the drop length becomes 2.7 m, with the same effect: fewer usable drops per roll, more rolls overall.
Frequently Asked Questions
Drops/roll = ⌊roll length ÷ (height+repeat)⌋; total drops = ⌈perimeter ÷ roll width⌉; rolls = ⌈drops ÷ drops-per-roll⌉. 18 m / 2.4 m → 9 rolls.
One ceiling-to-floor vertical strip. Estimating in drops is more accurate than area maths.
Add the repeat to the height — each drop is cut longer to match, so fewer drops per roll and more rolls.
Not for normal ones — drops still run beside them and the offcuts are wasted. Only deduct very large openings.
About 10 m long × 0.53 m wide (~5.3 m²) for UK/EU rolls. Check yours — both feed the calc.