CalculatorEnter your measurements below and it works the answer out.
Area divided by coverage, plus 15% waste, rounded up to whole rolls. Enter what you measured and pick how it is sold.
The arithmetic. Work out the area, divide by what one roll covers, add 15% waste, round up. Nothing more than that — the value of the page is the coverage figures and the waste allowance, both of which are stated here rather than hidden inside the tool.
Why the waste allowance is 15%. Fifteen per cent is the standard allowance because of the pattern repeat: every drop has to line up with the one beside it, and the offcut at the top of each strip is dead. A large repeat can push that to twenty.
How it is sold. Wallpaper is priced by the single roll but almost always sold in double rolls, which is where the confusion starts. A double roll is one continuous length of about 56 square feet, not two rolls in a bag.
Measure the openings honestly. Deduct large openings — a garage door, a picture window, a stairwell — and ignore small ones. Cutting a sheet or a board around a normal door wastes more material than the opening saves, which is why trades quote gross area and let the waste allowance absorb it.
Round up to how it is sold. A calculator that tells you 6.3 sheets is not finished. Everything below is rounded up to whole units, because that is what you can actually buy.
Divide your area in square feet by the coverage of one roll, then add 15% and round up. At 56 sq ft each, a 200 sq ft job needs 5.
15% is what this calculator adds. Fifteen per cent is the standard allowance because of the pattern repeat: every drop has to line up with the one beside it, and the offcut at the top of each strip is dead. A large repeat can push that to twenty.
With 8 ft ceilings the wall area is 384 sq ft. At about 56 usable square feet in a double roll with a 15% repeat allowance, that is 8 double rolls.