How To Calculate Wallpaper Needed

Wallpaper is sold by the roll but the calculation starts from wall area. The perimeter of the room times the ceiling height gives the total area of the four walls.

Doors and windows do not take wallpaper, so their area comes off the total. Subtracting them is what stops a room with two large windows from being over-ordered by a whole roll.

A roll covers far less than its gross area suggests. Offcuts for pattern matching, trimming and the ceiling line remove a surprising share, which is why the usable figure is often around 25 to 30 square feet.

The repeat length of the pattern matters. A large repeat needs each drop cut longer, so the usable area per roll drops and the roll count rises by one or two.

Roll widths differ. A wide roll covers more per drop, so the same room needs fewer rolls even at the same stated area per roll.

Always buy every roll from the same batch. Dye lots vary, and a roll bought later can sit visibly next to the ones already on the wall.

Order one spare roll. Damage, a bad cut and future repairs all need matching paper, and the pattern may be discontinued within a season.

Stairwells and bathrooms have odd shapes and awkward drops that waste more material than the arithmetic suggests, so add a roll to the calculated figure.

The ceiling is a separate calculation. Multiply the length by the width to get the ceiling area, then divide by the coverage of a roll in the same way.

Paintable wallpaper behaves the same way for the calculation but tolerates a sloppy pattern match, which lowers the spare you should hold back.

Wallpaper is hung in vertical strips called drops. Each drop is one full roll length long, and the number of drops follows from the perimeter divided by the roll width rather than from the area.

The usable length of a drop is reduced by the pattern repeat. With a twenty four inch repeat and a roll sixty feet long, roughly one drop in three ends up shorter than a full repeat and that offcut is waste.

Borders and friezes are quoted by the roll too, but they cover a run rather than an area. Measure the total length of wall where the border will go and divide by the length on the roll.

Rooms with a chimney breast or an alcove need the perimeter measured along the actual wall line, not around the outside of the room. Measuring around the outside buys several rolls more than the job needs.

Pasting machines have a limited table length, so a very long drop has to be booked folded. That wastes a little length each time and is one more reason to order a spare roll.