A common planning value is around 350–400 square feet per US gallon, but the product label is the source that matters. Coverage is affected by the coating, surface, roller nap, application method, and substrate.
Coverage is per coat
If a wall needs two coats, its area consumes coverage twice. A 400 sq ft wall with 400 sq ft/gal coverage needs about two gallons for two coats before waste—not one.
Porous surfaces use more
Fresh drywall, masonry, repaired areas, and rough texture can absorb more coating. Primer can reduce uneven absorption, but its own coverage also varies.
Exact volume versus shopping quantity
The formula produces a continuous volume, while stores sell discrete cans. Keep both numbers: exact volume explains the math; rounded containers form the shopping list.
Practical takeaway
Enter the actual label coverage and keep a modest contingency. Product-specific data beats a universal rule of thumb.
Related paint guides
How to measure a room for paint
Measure wall perimeter, height, ceilings, doors, and windows for a paint estimate you can audit.
Do I need one coat or two?
Choose a realistic coat count based on colour change, surface condition, sheen, and product instructions.
How to subtract doors and windows
Decide which openings are worth subtracting and keep trim calculations separate.