Measure Walls, Not the Room

Wallpaper covers walls, so the inputs are wall length and height, not floor area. Multiply per-wall area by the number of walls for gross area, subtract doors and windows, then add waste. The classic trap is buying for floor square footage — a 400 sq ft room can easily have 500+ sq ft of wall surface once all four sides are measured.

Waste Is Not Optional

Patterned wallpaper must be matched strip to strip, and every roll has trimmed edges and partial strips at corners and around openings. Plain paper needs ~5–10% waste; bold or half-drop patterns can eat 15–25%. Under-ordering by even one roll means a week-long delay and a possible dye-lot mismatch — buy the extra roll.

Coverage Labels Lie Slightly

A "double roll" covers about 56 sq ft of finished wall, but the label's number assumes perfect cutting with no pattern match. The calculator's roll coverage field defaults to 56 sq ft — enter the number from your specific roll, and remember that wallpaper is sold in double rolls far more often than singles, so a "roll" usually means two physical rolls.