One gallon of paint covers approximately 350–400 square feet. To find exactly how much you need, calculate the total wall area of the room, subtract openings, and divide by your paint's coverage rate.
The Formula
Wall Area = 2 × (Length + Width) × Height. Subtract 21 sq ft per door and 15 sq ft per window. Divide by coverage rate, then multiply by number of coats.
Coverage Rates by Paint Type
Flat/Matte — 400 sq ft per gallon (most coverage)
Eggshell — 375 sq ft per gallon
Satin — 350 sq ft per gallon
Semi-Gloss — 300–350 sq ft per gallon (lower porosity)
Primer — 200–300 sq ft per gallon (more absorption)
Pro Tips for Accurate Paint Estimation
Always round up to the nearest whole gallon — you can't buy 0.7 of a gallon
Dark colors often require 3 coats; factor this into your bid
Textured walls (orange peel, knockdown) absorb more — reduce coverage by 10–15%
Buy from the same batch (dye lot) for large areas — colors vary between batches
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