Paint Coverage Calculator: How Many Gallons You Actually Need
A standard gallon of paint covers approximately 350-400 square feet with a single, even coat on a smooth, previously painted wall — the figure most paint cans print on the label as a baseline.
That number needs two adjustments for a realistic estimate: subtracting the area of windows and doors (which aren't painted), and multiplying by the number of coats needed, which is almost always two for anything other than a very minor touch-up or a color extremely close to the existing wall color.
Texture and Porosity Change Real Coverage
Textured walls, unprimed drywall, and porous surfaces like unsealed masonry all absorb more paint than a smooth, previously painted surface, which can drop real coverage to 250-300 square feet per gallon or lower — sometimes significantly lower on very porous surfaces.
Dark-to-Light or Dramatic Color Changes
Going from a dark existing color to a much lighter new one (or the reverse) often requires a third coat, or a tinted primer coat first, since two coats of the new color may not fully mask the old one otherwise. This is a common reason an initial paint estimate falls short mid-project.
Primer Coverage Differs From Paint Coverage
Primer is typically formulated to bond well with the surface rather than to build opaque color, and its coverage rate per gallon is roughly similar to paint on average but can vary more depending on the primer type (standard vs. stain-blocking vs. bonding primers all behave differently on absorbent surfaces).
Frequently Asked Questions
How many square feet does a gallon of paint cover?
Roughly 350-400 square feet per coat on a smooth, previously painted surface — the number printed on most paint cans. Textured, porous, or unprimed surfaces cover meaningfully less per gallon.
Do I need to subtract windows and doors from my total?
Yes — window and door area isn't painted (aside from trim, which is usually calculated separately), so subtracting it from your total wall square footage before calculating gallons needed avoids over-ordering.
Why do textured walls need more paint?
Textured, porous, or unprimed surfaces absorb more paint than a smooth, previously painted wall, which can drop real coverage well below the 350-400 square foot per gallon baseline printed on the can.
Is primer coverage the same as paint coverage?
Roughly similar on average, but it varies more by primer type — standard, stain-blocking, and bonding primers behave differently on absorbent surfaces, so checking the specific product's coverage rate is more reliable than assuming it matches your paint's coverage.
This article is for informational purposes only. See our disclaimer.