How to Measure Walls for Wallpaper Installation | Get the Right Amount Every Time

A single mis-measured wall can leave you one roll short on a Sunday afternoon or stuck with five extra rolls you can’t return. The fix is a consistent system that accounts for the ways real walls differ from perfect rectangles. Here’s the exact protocol that wallpaper pros use to get the count right on the first try.

What You Need to Measure Correctly

The right tool is a metal tape measure, not a soft cloth one. Cloth tapes stretch over time and bend around corners, introducing errors that compound across multiple walls. A standard 25-foot metal tape gives you the reach and rigidity this job demands. You’ll also need a pencil, a notepad, and a calculator.

Step-by-Step: How to Measure Each Wall

Every wall gets measured separately, even when two walls look identical. Walls in the same room can differ by half an inch or more at floor level, and that discrepancy eats into wallpaper alignment.

Width. Place the tape flush against one corner or trim edge and extend it to the opposite corner. Measure at the baseboard level — walls are usually widest there — and take a second reading about waist-high. Use the larger of the two numbers. Write it down, then repeat for every wall in the room. Finally, add all the individual widths together for your total wall width.

Height. Run the tape from the floor (or the top of the baseboard if you’re working above it) straight up to the ceiling. Measure in at least two spots per wall — near one end and near the other — because ceilings slope more often than you’d expect. Use the tallest measurement you get. For walls that meet a staircase, measure from the lowest point where the wallpaper will start to the highest ceiling point.

Add the allowance. Add 2 inches to both your total width and your tallest height measurement. That inch per side gives you room for trimming at the ceiling and baseboard.

Calculate the area. Multiply your adjusted height (in inches) by your adjusted total width (in inches). Divide the result by 144 to get the square footage. Example: an 8-foot wall is 96 inches. If your room’s total width is 480 inches, that’s 96 × 480 = 46,080 square inches, divided by 144 = 320 square feet.

How to Figure Out How Many Rolls You Need

Once you have the total square footage, multiply it by 1.15 to add a 15% buffer for pattern matching, trimming waste, and mistakes — the standard cushion professionals use. Never subtract square footage for doors or windows. Those openings create leftover strips that cannot reliably cover an adjacent wall, so the industry rule is to measure as if every wall were solid.

Now divide the buffered total by the coverage number printed on your wallpaper’s packaging — typically around 28 to 30 square feet per US single roll. Round up to the nearest whole roll. If the pattern repeat (the vertical distance before the design repeats) is larger than 18 inches, you may need to divide by 20 instead of the standard divisor because bigger repeats produce more offcut waste.

For patterned wallpaper, a more precise method is the “drops” calculation. Divide your total wall width by the wallpaper’s width (commonly 21 inches for US rolls) and round up to get the number of vertical strips needed. Then divide the roll’s length (standard is about 33 feet) by your adjusted wall height and round down. Dividing strips needed by strips per roll gives you the roll count — and always add one extra roll for future repairs.

Once you have your final roll count, browse a selection of affordable wallpaper options that fit your budget before you start cutting.

Common Errors That Waste Material

The most expensive measurement mistake is using the smallest dimensions instead of the largest. Walls bow inward at the middle; a tape flush at bookend corners can read short by an inch or more. Always use your peak measurements.

The second most common error is subtracting openings. A standard door opening looks like a saving on paper, but the paper you “save” cannot bridge the adjacent full-height strip. Treat every wall as a solid rectangle and let the 15% buffer handle the overage.

Finally, never round down. A partial roll is not purchasable; rounding up is the only safe move.