How this wallpaper calculator works
The wall area is the room perimeter (2 × length + 2 × width) multiplied by wall height, minus doors and windows. Divide that area by the coverage printed on the roll — typically about 56 square feet for a standard American double roll — and add a waste allowance. For plain wallpaper 10% is enough; for wallpaper with a bold pattern repeat, 15-25% is safer because every strip must line up.
Always measure the actual wall height including baseboard and ceiling line — a room that is 8 feet 6 inches tall needs longer strips than the 8-foot assumption will give you. Buy one extra roll when the budget allows: dye lots can differ between batches, and an extra roll guarantees you can finish a future repair.
Buying tips
- Order the same dye lot batch number on every roll — color can vary between batches.
- Calculate per wall if the room has lots of niches or angled walls.
- Store leftover rolls flat, not standing, to avoid creasing.