Figuring out how much siding your house needs is a fairly straightforward calculation. Start by measuring each side’s length and width and multiply the two numbers. When you have measured all the sides, add the numbers together. Then calculate the length times width of windows, doors, and other areas that will not be covered by siding. Subtract this number from the first number. This will give you the rough square footage you will need.

Next, you will have to adjust that number for waste and the overlap of the siding, if there is any. The standard to add is 10 percent, but if your roof is steeply pitched or your house has angles that will require a great deal of cutting, add 15 percent. Finally, check with the manufacturer of the siding your are purchasing to see how much you should add for the pattern you are choosing. Most sidings come with charts to help you make that calculation.

The way various sidings are sold depends on the material. Vinyl and aluminum are usually sold by the square foot and trim pieces by the linear foot. Plywood and hardboard are sold per square, which is 100 square feet.