Measuring a house for siding is simply determining the area the sides of the house occupy and calculating how much siding to purchase to cover that area. Siding is bought and sold in square feet, and the calculations for that are included.
Things You'll Need
 50foot or longer tape measure
 Ladder
 Notepad and pencil
 Calculator
 Helper

Measure the length and height of each side of the house in feet, and write the measurements down. At gable ends, measure the height and width of the the gable. Be sure to mark gable measurements as such. Round all measurements to the nearest half foot. 12 feet 4 inches = 12.5 feet. 12 feet 2 inches = 12 feet. 12 feet 10 inches = 13 feet.

Multiply the height of each side by the length of each side. The result is the area of that side. Write these calculations in a column. For gable sections, multiply the height and width of the gable area, then divide by 2. Add gable areas to the area column as well.

Add the figures from the area column into a single figure. This figure should include the gable calculations. The sum of the column is the base area (Ba) to be sided in square feet. This number determines how much underlying material is to be used such as housewrap, for example.
Tips & Warnings
 Don't bother subtracting for standard windows and doors. However, large picture windows or sides where windows make up large portions of the wall should be subtracted. Add five to 10 percent for waste and short ends. You don't want to end up using a lot of short pieces at the end of the job to make up a shortfall. The area of a right triangle is base multiplied by height, divided by 2. This will work for any triangle if you divide it in two and make calculations for two triangles. For gables ends that are equal, this becomes [(H x W/2) / 2] x 2 or (H x W) / 2.