How Many Square Feet Does a Gallon of Paint Cover?
One gallon of paint covers 350–400 sq ft per coat on smooth primed drywall. The actual number depends on the surface texture, porosity, application method, and the specific product. Here is what the major brands publish — and how to apply the right number for your project.
Coverage by paint type and surface condition
| Surface / product type | Coverage per gallon | Notes |
|---|---|---|
| Smooth, primed drywall | 350–400 sq ft | Standard; use 350 as planning default |
| Light texture / orange peel | 300 sq ft | More surface area per sq ft of floor |
| Heavy texture / unprimed | 250 sq ft | High absorption or deep texture |
| Primer (bare drywall) | 200–250 sq ft | Porous surface absorbs primer |
| Primer (sealed surface) | 250–300 sq ft | Less absorption on primed or painted |
Coverage by brand (manufacturer-published)
| Brand | Published coverage | Source |
|---|---|---|
| Sherwin-Williams | 350–400 sq ft/gal | SW Paint Calculator FAQ |
| Benjamin Moore | 400 sq ft/gal | BM Paint Calculator |
| Behr | 350–400 sq ft/gal | Behr How-To Guide |
| KILZ Primer | 200–300 sq ft/gal | KILZ Calculator |
Always verify against the specific product label — formulations change. These are the planning figures current as of 2026.
Try the calculator with your room
Room Dimensions
Openings & Coats
How the math works
Step 1 — gross wall area
gross_wall = 2 × (length + width) × ceiling_height Step 2 — subtract openings
paintable = gross_wall − (doors × 20) − (windows × 15) Each standard 36×80 in door = 20.0 sq ft. Average window = 15 sq ft (industry convention). Paintable area is clamped to ≥0.
Step 3 — gallons
gallons_to_buy = ⌈ (paintable × coats) ÷ coverage ⌉ Coverage defaults to 350 sq ft/gal — the conservative figure used by Sherwin-Williams, Benjamin Moore and Behr field guides. Always round up to whole gallons; running out mid-job risks a dye-lot mismatch.
Frequently Asked Questions
400 sq ft/gal is achievable under ideal conditions: perfectly smooth, factory-primed drywall applied with a quality 3/8-inch nap roller using proper technique. Most real jobs land at 350 sq ft/gal or less because of texture, suction variation, overlapping roller strokes, and tray loss. 350 is the safe planning number.
Primer penetrates and seals porous surfaces (bare drywall, raw wood). The absorption is by design — it's what makes primer work. Topcoat paint applied over sealed primer sits on top rather than soaking in, which is why it achieves 350–400 sq ft/gal versus primer's 200–300 sq ft/gal.
The published ranges are nearly identical (350–400 sq ft/gal for all three), but formulation quality varies. Premium lines (SW Emerald, BM Aura, Behr Marquee) tend to have better pigment load and may cover in fewer coats. Budget lines may need an extra coat for color change. Coverage per gallon is similar; coats needed differs.
Heavier texture increases the real surface area beyond the flat footprint. A smooth flat wall gets 350–400 sq ft/gal. Light orange-peel or knockdown texture: ~300 sq ft/gal. Heavy texture or unprimed surface: ~250 sq ft/gal. The interior paint calculator on this site lets you choose the right coverage for your surface.
Calculate each color's wall area separately. For an accent wall (one wall of a 12×12 room): that wall is 12 × 8 = 96 sq ft. Two coats at 350 sq ft/gal = 0.55 gallons → buy 1 gallon. For the remaining three walls: 384 − 96 − openings (50 sq ft) = 238 sq ft for two coats = 1.36 gal → buy 2 gallons.