Most paints for general consumer use cover about 400 square feet per gallon. This amount is maximum coverage on a well prepared surface with no heavy texture or other abnormalities. If you are facing a stucco or other kind of unfamiliar surface, and it’s a big job, the best way to calculate the coverage of the paint is to do a test.
Remove all loose debris and properly prime the surface to get the maximum coverage out of your paint.
Measure out 16 ounces of your selected paint and put it in the roller tray.
Apply the paint to your prepared and primed surface using the roller. A thick napped roller may be required for surfaces with a lot of texture. Try to keep the application rectangular so it will be easier to measure.
Measure the length and width of the area covered by the paint.
Multiply the length by the width to get the paint coverage. For example, if you were able to cover a rectangle 5 feet by 6 feet, that equals 30 square feet.
Multiply your coverage from step 4 by eight to get your paint coverage for one gallon of paint. Once the paint is dry, you should also be able to assess whether or not you will need a second (or potentially third) coat for full coverage.