How much exterior paint do I need?

Exterior paint by house size and siding type

Each row is a one-story rectangular house with 9 ft walls and a 6/12 gable at each short end. The area is the walls plus the gable triangles, less 2 doors and 10 windows. Gallons are for 2 coats; primer is one coat on bare wood. Each figure is rounded up to whole gallons, with the exact amount in brackets.

The siding column covers wood, fiber-cement and hardboard siding. A two-story house has about twice the wall area and the same gables, so roughly double the siding column. For the area of a single wall or an unusual shape, the siding calculator does the geometry.

Measuring walls and gables for paint

Walk the house with a tape and add up the length of every wall you will paint. Multiply by the height from the bottom of the siding to the soffit. Each gable end adds a triangle: half its width times its rise. Take out garage doors, patio doors and big windows by measuring them; small windows hardly matter, because you paint around them anyway.

For a 28 × 48 ft house:

1. Walls: 152 ft of wall × 9 ft = 1,368 ft².
2. Gables: rise = 14 × 6/12 = 7 ft; 2 × ½ × 28 × 7 = 196 ft².
3. Openings: 2 doors × 21 + 10 windows × 15 = 192 ft², leaving 1,372 ft².
4. Paint: 1,372 × 2 ÷ 300 = 9.15 gallons, so buy 10 for lap siding, or 1,372 × 2 ÷ 225 = 12.20, so 13, for stucco.

Trim, soffits, fascia and doors

Trim is measured in lineal feet and converted to area at about 0.5 ft² per foot, a 6 in face. On the same house:

• Window and door casing: 10 windows × 16 ft + 2 doors × 17 ft = 194 ft.
• Corner boards: 4 corners × 9 ft = 36 ft.
• Fascia: both eaves, 96 ft, plus the four sloped rakes, 62.6 ft, = 158.6 ft.

That is 388.6 ft × 0.5 = 194 ft² of trim. 2 coats at 400 ft² per gallon is 0.97 gallons, so about 4 quarts or a gallon of trim colour.

Soffits are measured as length × depth. A 12 in soffit under the same 158.6 ft of eaves and rakes is 159 ft². 2 coats at 300 ft² per gallon is 1.06 gallons: a gallon and a quart. Vented vinyl or aluminum soffit is usually left unpainted.

Doors are counted one face at a time. Two 3 × 7 ft entry doors are 42 ft² outside; 2 coats take 0.21 gallons, so one quart. A 16 × 7 ft steel garage door is 112 ft² flat; at 400 ft² per gallon, 2 coats take 0.56 gallons. Raised panels add surface, so round up.

Primer, coats and what changes the number

Bare wood gets one coat of primer before the two finish coats: 1,372 ÷ 300 = 4.57 gallons, so 5, on the example house. New or uncoated stucco and masonry take a masonry primer at about 200 ft² per gallon, 7 gallons there. Cedar and redwood bleed tannin, a brown stain that can show through; spot-prime them with the stain-blocking or oil-based primer your paint maker names.

Repainting the same colour over sound paint can be one coat. That halves the figure: 4.57 gallons, so 5, on the 28 × 48 ft house. Big colour changes need two coats, sometimes over a tinted primer.

Rough surfaces drink paint. Rough stucco can drop to about 125 ft² per gallon, which turns 13 gallons into 22 on the example house. Rough-sawn wood behaves the same way.

Spraying costs paint. Spraying uses 20–30% more paint than rolling because of overspray. Back-rolling after spraying works the paint into rough siding.