Measure the length along the base of each exterior wall of the house. Write all the measurements down.
Measure the height of each exterior wall. The easiest way to do this is to measure a section of siding boards or bricks, then multiply that measurement by the number of sections. Typically you can assume that exterior walls measure 10 feet per story, but this is not always the case.
Calculate gables or peaks by multiplying the width of the gable by the height, then divide it by 2.
Multiply the length of the walls by the depth of the eaves (the overhang below your roof line).
Multiply the length of each exterior wall by its height, and add those figures together. Add the square footage of each gable and your eaves to this figure for the total square footage of the surface.
Assume you will get between 250 and 350 square feet of coverage per gallon of exterior paint. If the surface is rough, such as stucco or brick, your coverage will be closer to 250 square feet. Smooth siding such as vinyl or aluminum won't require as much paint. Divide your total square footage by the expected per-gallon coverage to get the number of gallons you will need for one coat of paint.
Estimate how much trim paint you will need. The Kelly-Moore Paint Co. suggests figuring 1 gallon of trim paint per 8 gallons of siding paint.
Things You Will Need
- Tape measure
- Unless you are painting over a sound surface with a very similar color and sheen (gloss level) of paint, two coats of paint will look better and be more durable. Double the number of gallons you estimated for a single coat of paint for two coats.
- The method of application will affect how much paint you use. Spraying paint will use more than using a roller and brush.
- Unless you have numerous or very large windows, don't deduct the windows and doors from your square foot count. You'll want to have a little paint left over to save for touch-ups.