Wallpaper Calculator

Two steps. First, how many vertical strips (drops) go around the room: perimeter ÷ roll width. Then how many drops you get from one roll: roll length ÷ drop length, where the drop length is your ceiling height plus a few inches to trim. Divide and round up. A 13 × 10 ft room (46 ft / 14 m around) with 9 ft (2.7 m) ceilings, papered with a plain 33 ft × 20.5 in (10.05 m × 53 cm) roll, needs about 27 drops at 3 drops per roll — 9 rolls. The calculator does it for any room and roll, and adds a waste allowance.

A lot. With a plain paper a drop is just your wall height plus trim. With a pattern, every drop has to be cut to a whole number of repeats so the pattern lines up between strips — so a 25 in (640 mm) repeat means each drop is rounded up to the next multiple of the repeat and the offcut is wasted. A big repeat can cost you an extra roll or two. Enter the repeat from the roll label and the calculator lengthens each drop accordingly.

Usually no. You still hang full drops across a doorway or window and cut the paper out afterwards, and those offcuts are what the waste allowance covers. Only deduct genuinely full-height openings — a run of sliding doors, or an open stairwell wall — using the openings field, which trims that width off the perimeter.

The most common worldwide is 10.05 m × 53 cm — about 5.3 m² (57 sq ft). In the US, paper is usually sold as a double roll of around 11 yards × 20.5 in (roughly 56 sq ft), even though it is priced as two singles. Sizes vary by brand, so read the length and width off your roll or the listing and enter them; the presets give you a starting point.

Add about 10–15%, and never fewer than one spare roll. You lose paper to trimming, pattern matching, mistakes and the odd damaged length, and a repair years later needs paper from the same batch. Buy it all at once and check the batch (or run) numbers match — batches can differ slightly in shade.

On a straight (straight-across) match the pattern sits level across every drop, so adjacent strips start at the same point. On a drop (offset) match, alternate drops are shifted by half the repeat, which staggers the pattern and wastes a little more at the top of every other strip. Both are handled by entering the pattern repeat; for a drop match, lean towards the higher end of the waste allowance.