CoatQuotaHow much paint a room takes, coat by coat.

Paint for a 11 × 8 ft room with 8 ft ceilings on wood siding, 2 coats

Paint needed
1.67gallons
268 ft² of wood siding in 2 coats — buy 2 gal
Paint by coat0.89 galfirst coat0.78 galeach later coat15% further once the surface is sealed — 0.12 gal saved1.67gallons total300 ft²/galon this surface
Paint1.67gal
What to buybuckets only pay from about 3.6 gal2 × 1 gal
Wall area304 ft² less 1 door and 1 window268ft²
Spread rategrain and end grain drink more than they look like they will300ft²/gal
First coat0.89gal
Each later coat14.999999999999991% further — the surface is sealed now0.78gal
Doubling the first coat would say0.12 gal more than you need1.79gal
Masking tape69 ft of edge260 yd rolls
Room length
11 ft
Room width
8 ft
Ceiling height
8 ft
Surface
wood siding
Coats
2
Doors
1

What to buy

1.67 gallons — 2 × 1 gal.

268 ft² of wall after openings, at 300 ft² per gallon on wood siding.

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. wood siding takes about 300, 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. 2 coats here comes to 1.67 gallons — not 1.79, which is what doubling the first coat would say.

That difference is 0.12 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 1.67 gallons of wall paint typically takes under a quart of trim enamel.

Cutting in is the job

69 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.** Wood siding takes about 300 ft² per gallon — grain and end grain drink more than they look like they will. The "400 square feet" on the tin is measured on smooth primed drywall, which is the best case and rarely the case.
  • **The second coat is cheaper than the first.** Once the surface is sealed, paint spreads about 14.999999999999991% further. 2 coats here is 1.67 gal, not 1.79 — doubling the first coat over-buys by 0.12 gal, which at retail is real money left in the garage.
  • 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 1.67 gal of wall paint typically takes under a quart for the trim.
  • Cutting in is where the time goes, not rolling. 69 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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