How Many Gallons of Paint Do I Need?
Measure walls, subtract doors and windows, and account for coats and real-world coverage.
Measure the wall area
For each room, add the lengths of all walls to get the perimeter, then multiply by the wall height. A 12 × 14 ft room has a 52 ft perimeter; with 8 ft walls that is 416 sq ft.
Subtract openings: about 21 sq ft for a standard door and 15 sq ft for an average window. With one door and two windows, 416 becomes 365 sq ft.
Coverage is a range, not a promise
Labels usually claim 350–400 sq ft per gallon on smooth, primed surfaces. Textured walls, fresh drywall and dark-to-light color changes all reduce it. Two coats double the paint needed.
365 sq ft × 2 coats ÷ 350 sq ft per gallon ≈ 2.1 gallons. Buying 2 gallons and a quart covers it.
When to prime
Prime new drywall, patched areas, stains, bare wood and glossy surfaces. Repainting a similar color over sound paint often needs no primer at all.