painting calculations

I need to paint a 2800 sf house. A man at Shermin Williams said I need to calculate 1 gallon/400sf for walls one coat.

Are those caculations resonable?

Depends on if you are using Wally world paint or Benjamin Moore, what type of rollers, and experience you have. Inexperienced people generally load too much paint on the roller and use more.

Sounds about right. Most paint companies recommend 350 to 400 sq ft per gallon. Depending on condition, colors, etc, you may need two coats. The second usually give better coverage of a larger area.