Paint coverage per gallon: what 350 sq ft really means
Every can quotes a coverage figure. Every room finds a way to beat it. Here is what the number assumes, and how to plan a room that does not need a third trip to the paint desk.
The planning number: 350 sq ft per gallon
Manufacturers usually claim 400 sq ft per gallon per coat. That figure is measured on a smooth, sealed, white-painted test panel under lab conditions. In a real room, 350 is the number that survives contact with texture, colour changes and a roller that is slightly too dry.
Use 400 only if you are recoating the same colour on smooth walls. Use 300 if the walls are textured or the new colour is much darker than the old one.
Coverage by surface
| Surface | Planning coverage | What changes it |
|---|---|---|
| Smooth, previously painted | 375–400 sq ft | Same colour family, sealed surface |
| Typical painted drywall | 350 sq ft | The default planning figure |
| Orange peel / knockdown texture | 300 sq ft | More surface area per square foot |
| Bare or patched drywall | 250 sq ft | Absorption — always prime first |
| Brick, block, stucco | 150–250 sq ft | Deep pores, heavy absorption |
What reduces coverage in practice
- Colour change. Going from a dark wall to a light one often needs three coats, and the first one covers far less than the label claims.
- Texture. A knockdown wall can easily be 15% more surface than a flat one. The paint does not know your tape measure, it knows the surface.
- Application method. Spraying wastes 10–20% to overspray, brushing uses more than rolling, and a roller that is too dry pushes paint around instead of depositing it.
- Thinning. Adding water to stretch a can buys you coverage and costs you durability. Do not do it for a finish coat.
- Porous substrate. New drywall, joint compound and bare wood soak up the first coat almost entirely.
From square footage to gallons
The formula is simple once you have the paintable area:
- Perimeter = 2 × (room length + room width).
- Wall area = perimeter × ceiling height.
- Subtract roughly 21 sq ft per door and 15 sq ft per window.
- Multiply by the number of coats.
- Divide by 350, then round up.
| Room | Walls (8 ft ceiling) | 2 coats | Gallons to buy |
|---|---|---|---|
| 10 × 10 ft bedroom | ~264 sq ft | 528 sq ft | 2 gal |
| 12 × 14 ft bedroom | ~344 sq ft | 688 sq ft | 2 gal |
| 16 × 20 ft living room | ~504 sq ft | 1,008 sq ft | 3 gal |
| 20 × 30 ft open plan | ~728 sq ft | 1,456 sq ft | 5 gal |
These figures assume two doors and two windows per room. A room with a wall of glass needs noticeably less; a hallway with six doorways needs more than its size suggests.
One coat or two?
Two, for anything that will be looked at in daylight. One coat is only defensible when you are refreshing the identical colour over sound paint — and even then, the first coat over a scrubbed wall often looks thin at the edges.
Primer is a separate question. Prime bare drywall, patched areas, bare wood, and any wall going from dark to light. Paint-and-primer products are fine over existing paint but are not a substitute for primer on raw substrate.
Buying tips
- Buy a quart for touch-ups, not a gallon. A quart covers about 90 sq ft, enough for a full accent wall.
- Mix cans together. If you buy three gallons, box them in one container so any slight tint difference disappears.
- Keep the label. The product code is the only way to get an exact match two years later.
- Ceilings need less. One coat of ceiling paint over an existing white ceiling is usually enough; going from colour to white needs two.