To calculate the amount of siding you will need to cover a wall, you need to know the square footage of the wall, and if you are planning to deduct for openings in the wall, the size of windows and doors. If there are only a few smaller openings in the wall, then ignore them. You more than likely waste the same amount of material as you are saving.
wall length = 26 feet wall height = 9 feet window = 5 feet x 4 feet door = 3 feet x 6 feet and 8 inches The siding we are using here is a Fibre-cement board, 144 inches long and 8 1/4-inch wide. We will install it with a 1 1/4-inch overlap, giving it an exposed face of seven inches.
26 * 9 = 234
Your wall has a total area of 234 square feet.
5 * 4 = 20
The window opening is 20 square feet.
36 * 80 = 2880
2880 ÷ 144 = 20
The door opening is 20 square feet.
Total openings equal 20 + 20 = 40 square feet.
234 - 40 = 194
There are 194 square feet of wall area you have to cover with siding.
12 ÷ 7 = 1.743
This siding has a lineal foot factor of 1.743.
194 * 1.743 = 338.142 rounded to 339
You will need 339 lineal feet of siding
339 ÷ 12 = 28.25 rounded to 29
You will need 29 boards of siding to cover the wall.