Strips and repeat
Strips are the wall width divided by the roll width, rounded up. Each strip can lose one pattern repeat when you match the next drop. That loss is strips × repeat × roll width, in feet. Add it to the wall area, then divide by the square feet printed on the roll.
56 square feet in the form is only an example of a double roll. Your roll may say something else. Paint for the same wall is the paint calculator. The bare area is the square foot calculator.
FAQ
How many rolls?
Divide wall area by the square feet on the roll label, then add the pattern. A random match can use repeat of 0. A drop match wastes about one repeat length on every strip.
Do I subtract doors?
Yes, before you type the wall area. A door you paper over does not come off. Windows you paper around do.
Sources
- NIST Handbook 44: Inch and foot used to turn roll width and repeat into square feet. The roll’s own label is the coverage.