How to Calculate How Many Rolls of Wallpaper You Need
I built this wallpaper calculator to help you get the roll count right before purchasing — because wallpaper dye lots vary between print runs, and running short means hunting for matching rolls that may no longer exist. The calculation is more complex than paint because you need to account for wall height, roll width, usable length per roll, and pattern repeat — all of which interact to determine how many rolls you actually need.
The basic approach: measure the perimeter of the room (total width of walls to be papered), subtract openings (doors and windows), then calculate how many strips you can cut from a single roll based on the wall height and roll length. The pattern repeat adds extra waste because each strip must be aligned to the same point in the repeat — the longer the repeat, the more you waste per strip.
Understanding Pattern Repeats and How They Affect Quantity
Pattern repeat is the vertical distance between two identical points in the wallpaper design. When matching a patterned paper, each strip must start at the correct point in the pattern, which means cutting off the excess at the top of each strip. Here's how repeat length affects waste:
- No repeat (plain or texture): no pattern waste — only the standard trim at top and bottom.
- Small repeat (under 4 inches): minimal waste; almost every cut-off can be used on the next strip.
- Medium repeat (4–18 inches): add 15–20% to your roll count for pattern matching.
- Large repeat (over 18 inches): can waste up to one full repeat per strip; add 20–30% extra rolls.
Tips for Wallpaper Installation
The most important preparation step is sizing the walls — applying a diluted wallpaper paste or dedicated size solution before hanging. Sizing reduces porosity, prevents the wall from absorbing paste too quickly, and makes it much easier to slide and reposition strips. Skipping this step on new drywall or heavily patched walls is a very common mistake that leads to bubbling and poor adhesion.
Always start from a perfectly plumb vertical line, not from a corner — corners are almost never truly vertical. Use a spirit level or laser level to draw a plumb guide line 1 roll-width from the corner. Hang the first strip to this line, then work away from it in both directions. The last strip at the opposite corner will likely need to be trimmed, and the pattern may not align perfectly — this is expected and usually hidden by the corner or by trim.
Frequently Asked Questions
How wide and long is a standard wallpaper roll?
European rolls are most commonly 52 cm (about 20.5") wide and 10 metres (about 33 feet) long, giving approximately 5.5 square metres per roll. US rolls are often 27 inches wide and 13.5 feet long (about 30 square feet per double roll). Always check the label — roll sizes vary significantly by manufacturer and product line. The calculator uses the specific dimensions you enter, so always measure your actual rolls before buying.
Can I wallpaper over existing wallpaper?
Professionals strongly advise against it. Hanging new wallpaper over old adds weight, traps moisture, and can cause the old paper to bubble or peel — taking the new paper with it. The seams of the old paper also telegraph through and are visible in the new surface. Remove old wallpaper using a scoring tool and wallpaper stripper solution, then repair and prepare the wall before re-papering. It's more work upfront but the result is far superior and longer-lasting.
What is paste-the-wall wallpaper?
Paste-the-wall (PTW) wallpaper is applied by pasting the wall rather than the back of the paper, which makes installation significantly easier. The paper doesn't need to soak or expand before hanging, there's no paste table required, and strips are lighter and easier to handle. PTW papers are ideal for DIYers and are increasingly the standard format for high-quality designer wallpapers. Traditional paste-the-paper (PTP) installation is still used for delicate papers like grasscloth and some vinyls.
