CoatQuotaHow much paint a room takes, coat by coat.

Paint for a 15 × 11 ft room with 10 ft ceilings on primed drywall, 1 coats

Paint needed
1.29gallons
484 ft² of primed drywall in 1 coat — buy 2 gal
Paint by coat1.29 galfirst coat1.12 galeach later coat15% further once the surface is sealed — 0 gal saved1.29gallons total375 ft²/galon this surface
Paint1.29gal
What to buybuckets only pay from about 3.6 gal2 × 1 gal
Wall area520 ft² less 1 door and 1 window484ft²
Spread ratethe surface the label figure is measured on375ft²/gal
First coat1.29gal
Each later coat14.999999999999991% further — the surface is sealed now1.12gal
Masking tape83 ft of edge260 yd rolls
Room length
15 ft
Room width
11 ft
Ceiling height
10 ft
Surface
primed drywall
Coats
1
Doors
1

What to buy

1.29 gallons — 2 × 1 gal.

484 ft² of wall after openings, at 375 ft² per gallon on primed drywall.

Spread rate belongs to the surface, not the tin

The "400 square feet per gallon" printed on a can is measured on smooth primed drywall. primed drywall takes about 375, and that difference is the single biggest reason people run out.

Rough and porous surfaces are worst: stucco can halve the figure on the label.

The second coat is cheaper than the first

Once the surface is sealed, paint spreads about 15% further. 1 coats here comes to 1.29 gallons — not 1.29, which is what doubling the first coat would say.

That difference is 0 gallons of paint that would sit in the garage until it went off.

Box it before you start

Pour every tin into one bucket and mix. Tins of the same color from different batches differ slightly, and a wall painted from two tins shows the join exactly where you stopped for lunch.

Trim does not scale with the room

Doors, trim and ceilings are linear-foot work and a completely separate calculation. A room needing 1.29 gallons of wall paint typically takes under a quart of trim enamel.

Cutting in is the job

83 ft of edge here — that is where the hours go, not the rolling. A good 2½″ angled sash brush beats tape on most edges; tape earns its place mainly against carpet and glass.

Notes

  • **Spread rate is a property of the surface, not the paint.** Primed drywall takes about 375 ft² per gallon — the surface the label figure is measured on. The "400 square feet" on the tin is measured on smooth primed drywall, which is the best case and rarely the case.
  • One coat only works over a similar colour on a sealed surface. Anything else — new drywall, a colour change, a patch repair — needs two, and trying to make one heavy coat do the job of two gives you runs rather than coverage.
  • Buy all of it in one go and box it — pour every tin into one bucket and mix. Tins of the same colour from different batches differ slightly, and a wall painted from two tins shows the change where they met.
  • Trim, doors and ceilings do not scale with floor area — they scale with linear feet, and they are a separate calculation. A room that takes 1.29 gal of wall paint typically takes under a quart for the trim.
  • Cutting in is where the time goes, not rolling. 83 ft of edge here. A decent 2½″ angled sash brush and a steady hand beat tape on most edges, and tape is worth it mainly against carpet and glass.

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