How to Calculate Paint
Calculate the total wall area by adding the room's perimeter (2 × length + 2 × width) and multiplying by the ceiling height. Subtract 21 square feet per door and 15 square feet per window. One gallon of paint covers approximately 350 square feet per coat. Most paint jobs require 2 coats for even coverage, especially when changing colors.
Tips for Accurate Estimation
Textured walls absorb more paint — add 15–20% to your estimate. Dark-to-light color changes may need 3 coats or a tinted primer. Round up to the nearest whole gallon since you'll want extra for touch-ups. Store leftover paint in a cool, dry place for future touch-ups — it lasts 2–10 years sealed.