General Measuring Guidelines
Measure your house in terms of how many SQUARE FEET of outside coverage area you have. Measure length of each wall including doors and windows. Find the total square feet of the wall(s) by multiplying total wall length.
If your house has gables, you can estimate by just adding 2 feet to the height when making your calculations. For more precision, measure the width of the gable wall and multiply that figure by its height. Divide the final figure by 2 to determine the gable’s square-foot dimensions.
Subtract areas that will not be covered or will use a different base (typically trim, doors, fascia, and soffits). Standard doors are about 3 x 7 feet or 21 square feet; standard windows about 3 x 4 or 12 square feet.
ROUND-UP to the nearest 100 square foot (e.g. 1833 goes to 1900).
DIVIDE BY 100 to get the TOTAL NUMBER OF GALLONS you’ll need on smooth to mildly rough surfaces.
NOTE ON SURFACES:
ADD 10% for cement block, cedar, stucco
SUBTRACT 10% for Masonite and other very smooth surfaces
If you have 2339 square feet, you’ll need 24 gallons, typically, so you’ll have to buy 25 gallons, or FIVE pails to complete the job.