Tip: Estimate for texture surfaces
As an estimator and project manager for one of the largest painting contractors in the state of Florida I recommend that when estimating the amount of paint that you need to take in to account the texture of the surface and the porosity of the surface. On the average you can expect to get around 250 sq. ft. per gallon on rough surfaces (i.e. stucco) and 300 sq. ft. per gallon on smooth drywall.