Wallpaper Calculator
Work out wallpaper drop length with pattern repeat and match, drops per roll, drops needed and rolls to buy, with an area-based cross-check for openings.
Interactive calculator · Method WALLPAPER-ROLLS-1.0 · Last reviewed: 2026-11-04
Calculate your scenario
Drop length = wall height × 12 + trimming allowance; for straight and half-drop match it is rounded up to a whole number of pattern repeats, and half-drop adds half a repeat per drop as a simple allowance for the offset.
Your inputs
Default worked example. Edit the inputs to calculate your scenario.
Default worked example
Drop = 100 in rounded up to whole 21 in repeats = 105 in; ⌊396 ÷ 105⌋ = 3 per roll; 27 drops ÷ 3 = 9 rolls.
How to use the calculator
Measure around the room along the walls you will paper and the wall height. Take roll width, roll length, pattern repeat and match type from the roll label, then add a trimming allowance and an extra allowance for mistakes.
What the result means
On 40 ft of 8 ft walls, a 21 in straight repeat makes each drop 105 in, so a 33 ft roll gives 3 drops. 24 drops plus 10% is 27 drops, or 9 rolls; the plain area check says 6, and the gap is pattern-repeat waste.
Formula and units
Drop length = wall height × 12 + trimming allowance; for straight and half-drop match it is rounded up to a whole number of pattern repeats, and half-drop adds half a repeat per drop as a simple allowance for the offset. Drops per roll = ⌊roll length × 12 ÷ drop length⌋. Drops needed = ⌈wall width × 12 ÷ roll width⌉ × (1 + allowance %), rounded up. Rolls = ⌈drops needed ÷ drops per roll⌉. Cross-check = ⌈(wall area − openings) × (1 + allowance %) ÷ roll area⌉.
Worked examples
40 ft of 8 ft walls, 21 in straight repeat: Total width of walls to paper: 40 ft; Wall height: 8 ft; Doors and windows area (used in the area cross-check): 21 sq ft; Roll width: 20.5 in; Roll length: 33 ft; Pattern repeat (0 for none): 21 in; Trimming allowance per drop (top + bottom): 4 in; Extra allowance for mistakes: 10 %; Pattern match: straight.
Example result: Rolls needed (drop method): 9 rolls; Drop length: 105 in (8.75 ft); Drops per roll: 3 drops; Drops needed (with allowance): 27 drops (24 before allowance); Rolls by area (cross-check): 6 rolls.
30 ft of 9 ft walls, 27 in rolls, 18 in half-drop: Total width of walls to paper: 30 ft; Wall height: 9 ft; Doors and windows area (used in the area cross-check): 0 sq ft; Roll width: 27 in; Roll length: 27 ft; Pattern repeat (0 for none): 18 in; Trimming allowance per drop (top + bottom): 4 in; Extra allowance for mistakes: 0 %; Pattern match: half.
Example result: Rolls needed (drop method): 7 rolls; Drop length: 135 in (11.25 ft); Drops per roll: 2 drops; Drops needed (with allowance): 14 drops (14 before allowance); Rolls by area (cross-check): 5 rolls.
Limitations and common mistakes
Assumptions: plain rectangular walls, every drop cut full height, no reuse of leftover pieces between drops, and openings ignored in the drop method (short drops above doors and windows can sometimes come from offcuts, which is why the area cross-check is lower). Half-drop and offset matches vary by product; follow the roll label. Rolls from different batches can differ in shade, so buy one batch.
Buying by area alone. With a large repeat each drop wastes part of a repeat, so the drop method usually needs more rolls than area suggests.
Sources and assumptions
Method WALLPAPER-ROLLS-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.