CoatQuotaHow much paint a room takes, coat by coat.

Exterior paint for 230 ft of shiplap siding at 20 ft high, 2 coats

Exterior paint
37.13gallons
4,468 ft² of grooved or shiplap siding in 2 coats — 8 × 5 gal buckets
Exterior paint by coat19.86 galfirst coat17.27 galeach later coat15% further once the surface is sealed — 2.59 gal saved37.13gallons total225 ft²/galtexture, not brand
Paint37.13gal
What to buybuckets pay from about 3.6 gal up8 × 5 gal
Wall area230 ft perimeter × 20 ft, less 6 windows and 2 doors4,468ft²
Spread ratethe grooves are extra surface, and they hold paint unevenly225ft²/gal
First coat19.86gal
Each later coat15% further on a sealed surface17.27gal
Doubling the first coat would say2.59 gal more than needed39.72gal
Perimeter
230 ft
Wall height
20 ft
Siding
shiplap siding
Coats
2
Windows
6

Texture decides the spread rate, not the brand

shiplap siding takes about 225 ft² per gallon. The same house in smooth fiber cement would take noticeably less, and in brick noticeably more — the mortar joints drink more than the brick does.

230 ft of perimeter at 20 ft high, less 6 windows and two doors, is 4,468 ft². At 2 coats that is 37.13 gallons.

The second coat is cheaper

Once the surface is sealed, paint spreads about 15% further. Doubling the first coat would say 39.72 gal — 2.59 gal more than you need, sitting in the garage until it separates.

Two weather limits matter more than the gallon count

Surface temperature has to stay above about 10 °C for the whole cure, not just while you are painting. A warm afternoon followed by a cold night gives a film that never properly coalesces, and it comes off in sheets the following spring.

Dew point matters as much as rain. Early-morning painting on a clear autumn day fails constantly for exactly this reason — the siding is wet with dew that you cannot see.

Wash first, and wait

Paint over chalky or dirty siding fails at the interface however good the paint is. Pressure-washed wood needs two or three dry days; a moisture meter reading under 15% is the honest test, not "it looks dry".

Back-roll anything you spray

Spray lays paint on the surface. Back-rolling works it into the grain and the grooves. On shiplap siding that is the difference between six years and twelve.

Notes

  • **Surface texture, not brand, decides the spread rate.** Grooved or shiplap siding takes about 225 ft² per gallon — the grooves are extra surface, and they hold paint unevenly. The same house in smooth fibre cement would take 12.77 gal per coat against 19.86 here.
  • **Two weather limits matter more than the gallon count.** Surface temperature must stay above about 10 °C for the whole cure, not just while you are painting — a warm afternoon followed by a cold night gives a film that never coalesces. And the surface has to be dry: dew point matters as much as rain, which is why early-morning painting on a clear autumn day so often fails.
  • On grooved or shiplap siding in sound condition, spot-prime bare and repaired areas rather than priming the whole wall. A full prime coat here buys very little.
  • Wash it first, and let it dry properly. Paint over chalky or dirty siding fails at the interface no matter how good the paint is, and pressure-washed wood needs two or three dry days before it is ready — a moisture meter reading under 15% is the honest test.
  • Back-roll anything sprayed. Spray alone lays the paint on the surface; back-rolling works it into the grain and the grooves, and on grooved or shiplap siding that is the difference between six years and twelve.
  • Buy it all at once and box it. Exterior walls are seen in full sun from a distance, which is the least forgiving lighting there is for a batch difference.

Nearby sizes

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