Gallons needed for walls and ceiling with waste factor.
One gallon of paint covers approximately 350 sq ft per coat on smooth surfaces. Rough textures, deep colors, and primer coats may require more. Doors are estimated at 21 sq ft each and windows at 15 sq ft each for the deduction.
Two coats are recommended for any color change. Going from white to a dark color often requires a tinted primer as the first coat to get true color in two coats.