Exterior Paint Calculator
Calculate gallons of exterior paint needed based on wall area, windows, doors, and coats. Enter values for instant results with step-by-step formulas.
Reviewed by Abdullah, Technical Content Specialist
Formula
Gallons = (Net Wall Area x Coats) / Coverage per Gallon
Where net wall area equals the total wall perimeter times height minus all window and door openings. Coverage per gallon is typically 350-400 sq ft for smooth surfaces and 250-300 for rough textures.
Worked Examples
Example 1: Single-Story Ranch House
Problem:Calculate paint for a 40x30 ft single-story house, 9 ft walls, 8 windows (12 sq ft each), 2 doors (21 sq ft each), 2 coats, 350 sq ft per gallon, $45/gallon.
Solution:Perimeter = 2 x (40 + 30) = 140 ft\nGross area = 140 x 9 = 1,260 sq ft\nWindow area = 8 x 12 = 96 sq ft\nDoor area = 2 x 21 = 42 sq ft\nNet area = 1,260 - 96 - 42 = 1,122 sq ft\nPaintable area = 1,122 x 2 coats = 2,244 sq ft\nGallons = 2,244 / 350 = 6.4 = 7 gallons\nCost = 7 x $45 = $315
Result:7 gallons | 1,122 sq ft net | $315 paint cost
Example 2: Two-Story Colonial
Problem:Calculate paint for a 45x28 ft two-story house, 9 ft walls per story, 14 windows (15 sq ft each), 3 doors (21 sq ft each), 2 coats, 350 sq ft per gallon, $50/gallon.
Solution:Perimeter = 2 x (45 + 28) = 146 ft\nGross area = 146 x 18 = 2,628 sq ft\nWindow area = 14 x 15 = 210 sq ft\nDoor area = 3 x 21 = 63 sq ft\nNet area = 2,628 - 210 - 63 = 2,355 sq ft\nPaintable area = 2,355 x 2 coats = 4,710 sq ft\nGallons = 4,710 / 350 = 13.5 = 14 gallons\nCost = 14 x $50 = $700
Result:14 gallons (2 x 5-gal + 4 singles) | 2,355 sq ft net | $700 paint cost
Frequently Asked Questions
How do I calculate how much exterior paint I need?
Start by measuring the perimeter of your house and multiplying it by the wall height to get the gross wall area. For a rectangular house, the perimeter is two times the length plus two times the width. Subtract the area of all windows and doors from the gross area to get the net paintable area. Multiply the net area by the number of coats you plan to apply (usually 2 coats for best coverage). Then divide the total paintable area by the paint coverage rate per gallon, which is typically 350 to 400 square feet for smooth surfaces and 250 to 300 for rough or textured surfaces. Always round up to the nearest whole gallon to ensure you have enough paint.
How many coats of exterior paint are recommended?
Two coats of exterior paint are recommended for the best coverage, durability, and color richness. A single coat often shows thin spots, roller marks, and the underlying color, especially when changing from a darker to a lighter color. The first coat acts as a base that fills the surface texture and provides a uniform foundation, while the second coat delivers full color opacity and creates a thicker protective film. Some situations require three coats: when covering very dark colors with light ones, when painting bare wood without primer, or when using highly transparent colors like reds and yellows. Using a tinted primer that approximates the finish color can improve coverage and potentially eliminate the need for a third coat.
What is the coverage rate for exterior paint?
Standard exterior latex paint covers approximately 350 to 400 square feet per gallon on smooth surfaces like vinyl siding, smooth wood, or previously painted surfaces in good condition. Rough or textured surfaces like stucco, brick, rough-sawn wood, or heavily weathered clapboard reduce coverage to 200 to 300 square feet per gallon because the texture absorbs more paint. Premium paints with higher solids content may cover slightly more area per gallon. The coverage rate also depends on application method: brushing uses slightly more paint than rolling, and spraying without back-rolling can use 15 to 30 percent more due to overspray. Always check the specific coverage rate listed on your paint can, as it varies between products and manufacturers.
Should I use primer before exterior paint?
Primer is recommended in several situations: painting bare wood or new construction, painting over stains (water, smoke, tannin bleed), switching from oil-based to latex paint, painting over very dark colors with light ones, or when the existing paint is chalking or deteriorating. A quality exterior primer seals the surface, blocks stains, promotes adhesion, and ensures uniform color absorption for the topcoat. Some premium exterior paints are marketed as paint-and-primer-in-one, which can work well over previously painted surfaces in good condition. However, for bare wood, new drywall, or problem surfaces, a dedicated primer always outperforms a self-priming paint. Tinting the primer to match the finish color reduces the number of topcoats needed, especially with bold or deep colors.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy