You generally measure the exterior of a house when you plan to order and install new exterior siding. Because it isn't necessary to know the exact size, generally you round the measurements up. If you need to know the exact size, it simply means that your math will be a little more difficult. The basic way to measure the exterior remains the same, and a homeowner can do it easily.
Things You'll Need
 Tape measure
 1/4inch graph paper
 Pencil
 Straightedge
 Calculator

Measure the front of the house. The shape of most homes are square, rectangular and triangular shapes. Look at the front of your house, and see the basic rectangular shape. Measure from the lowest spot in the grade to where the rectangular shape ends (typically at the roof). Roughly draw this shape on your graph paper, and round the height measurement to the nearest half foot. Example: 12 foot, 4 inches rounds to 12 foot, 6 inches.

Measure gables (the triangular shaped sections that look like triangles) by measuring from the peak to the top of the rectangle (typically at the roof line). This is the triangular height. Measure the full width of the bottom of the gable triangle. Sketch this shape on your drawing. It is often a good idea to label the sides (elevations) of your drawing to easily see which side is which. Round your measurements to the nearest half foot.

Calculate the area of any rectangular or square shape by the formula, length times height. Example: a 43foot wide house that is 12 feet, 6 inches tall at the roof line is 43 x 12.5 = 107.5. Remember that 6 inches is one half and represented on the calculator as .5 This is why you round to the nearest half footto do the calculations more easily.

Calculate the area of a triangle (any triangular shape) by using the formula height times length, divided by 2.

Continue around the house measuring every wall and projection in the same way. Use the formulas above to determine the area for each section, and add all of your sections together for the rough estimate of your exterior square footage.
Tips & Warnings
 For exact measurements convert your measurements into inches, and use the formulas. After adding all of your measurements together, convert your inches back into feet and your estimate will be accurate to the inch.
 Clearly indicate sloping yards and walkout basements on your drawing since undergrade exterior walls (walls covered in soil) are not calculated in most applications.