Published August 14, 2026 · Updated August 23, 2026 · By Tupep
1,500 square feet is a floor number, not a wall number
The square footage on your listing describes the floor, and paint goes on the walls. Those two numbers are not related by any reliable ratio, because a 1,500 sq ft ranch and a 1,500 sq ft two story have completely different amounts of siding. The two story has half the footprint, so half the perimeter, but twice the wall height, and it has smaller gable ends. In practice the two story usually needs slightly less siding paint than the ranch and a lot more setup.
So we throw the listing number away and rebuild the estimate from the footprint. It takes about ten minutes with a tape or a measuring wheel.
The exterior formula
- Wall area = footprint perimeter x wall height
- Gable area = 0.5 x gable width x gable rise, where rise = (half the width) x (pitch rise / 12)
- Net siding = wall area + gable area – half of the opening area
- Effective area = net siding x texture factor
- Gallons = (effective area x coats) / coverage rate
Two conventions in there are worth explaining. We deduct only half the window and door area on exteriors, because you spend real paint cutting the perimeter of every opening and trimming out around it, and full deductions consistently leave people a gallon short. And wall height is measured from the bottom of the siding to the soffit, which on an 8 foot ceiling house is usually about 10 feet once you add the rim joist and the frieze area, not 8.
Worked example: a 1,500 sq ft ranch
Footprint 30 ft x 50 ft, which is exactly 1,500. Wall height 10 ft. Gable ends on the two 30 ft walls at a 6/12 pitch. Twelve windows averaging 15 sq ft, two exterior doors at 20 sq ft each. Lap siding.
- Perimeter: 2 x (30 + 50) = 160 linear ft
- Wall area: 160 x 10 = 1,600 sq ft
- Gable rise: 15 ft x (6/12) = 7.5 ft. Gable area: 0.5 x 30 x 7.5 = 112.5 sq ft each, so 225 sq ft for two
- Subtotal: 1,825 sq ft
- Openings: (12 x 15) + (2 x 20) = 220 sq ft. Deduct half: 110 sq ft
- Net siding: 1,825 – 110 = 1,715 sq ft
- Lap siding texture factor 1.10: 1,715 x 1.10 = 1,887 sq ft effective
- Two coats: 3,774 sq ft. At 325 sq ft per gallon: 11.6 gallons
Buy 12 gallons of body color, which is two 5 gallon pails plus two singles. Most exterior acrylics state 250 to 400 sq ft per gallon, and 325 is a fair working number for lap siding that has been painted before.
Texture factors are the biggest single variable
The same measured wall can take twice as much paint depending on what it is made of. A gallon spread across rough cedar shakes is filling a surface with far more actual area than a gallon on smooth fiber cement.
| Siding type | Texture factor | Effective coverage per gallon |
|---|---|---|
| Smooth fiber cement, smooth hardboard | 1.00 | 325 sq ft |
| Vinyl or aluminum lap | 1.05 | 310 sq ft |
| Painted wood lap siding | 1.10 | 295 sq ft |
| Rough sawn cedar, T1-11 | 1.25 | 260 sq ft |
| Smooth or sand stucco | 1.30 | 250 sq ft |
| Cedar shakes, heavy dash stucco | 1.50 | 215 sq ft |
| Unpainted brick or split block | 1.75 | 185 sq ft |
Trim is a separate purchase and it is bigger than you think
Soffit, fascia, corner boards, and window and door casings add up fast on a house with a 1.5 ft overhang.
- Soffit: 160 linear ft x 1.5 ft = 240 sq ft
- Fascia: 160 linear ft x 0.7 ft = 112 sq ft
- Corner boards: 4 corners x 10 ft x 0.7 ft = 28 sq ft
- Window and door casings: 14 openings x 16 linear ft x 0.4 ft = 90 sq ft
- Total trim: 470 sq ft. Two coats is 940 sq ft, so 940 / 350 = 2.7 gallons. Buy 3 gallons of trim color.
That is a full 3 gallons of a second color that people routinely forget to price. On a two tone house it is often the same order of magnitude as a whole interior room repaint.
Two field realities that wreck the label spread rate
First, surface temperature and sun. Exterior acrylics have an application window most brands put around 50 to 90 degrees F, with low temperature formulas going lower, and the number that matters is the temperature of the siding, not the air. On a south wall in direct afternoon sun the substrate can be 30 degrees above air temperature, the film starts setting before you can spread it, and your gallon covers noticeably less while leaving lap marks. We chase the shade around the house and it changes both the finish quality and the material count.
Second, spraying is not free. Spraying an exterior is fast, but you lose material to overspray, wind drift, and the hose and pump. On an open exterior that loss commonly runs 20 to 40 percent, so if you are spraying, add roughly a quarter to your rolled estimate. Spraying porous or rough siding also needs back-rolling or back-brushing behind the gun, because atomized paint bridges over the texture instead of getting pushed into it, and a bridged film fails early.
One more thing on coats. If your house was last painted in the same color family and the existing film is sound, one coat may hold. If you are changing color, exposing bare wood in the prep, or working on the elevation that gets afternoon sun, budget two. The south and west sides weather fastest, and putting the extra film there is money better spent than an even coat everywhere.
Related guides
- Painting Light Over Dark: The Primer Math
- How Much Paint for a 12×12 Bedroom (Walls, Ceiling, Trim Separately)
- How Much Ceiling Paint for a Whole House
- How Many Sheets of Drywall for a 2-Car Garage
Sources and Further Reading
Run your own numbers with the Paint Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
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