How Much Paint Do I Need?
A gallon of paint typically covers about 350-400 square feet with one coat. For most rooms, two coats are recommended for even coverage and true color depth.
Start by calculating the total wall area: multiply the perimeter of the room by the ceiling height. Then subtract openings -- a standard door is about 21 sq ft, and a standard window around 15 sq ft.
Primer adds another coat layer if you are covering dark colors or painting new drywall. Textured walls can require 10-20% more paint due to the increased surface area.