Exterior Paint Calculator: How Many Gallons

This exterior paint calculator tells you how many gallons of paint you need for a house or building exterior. You enter the total wall area (in square feet or square meters), the number of coats, and the paint coverage per gallon; it returns the gallons required, plus the total liters and an estimate for primer. The first result is the exact gallons of paint for the job.

Formula

The basic formula is:

Gallons = (Wall Area × Number of Coats) ÷ Coverage per Gallon

Where:

• Wall Area – the total exterior surface you plan to paint, in square feet (or square meters).
• Number of Coats – usually 2 for a quality exterior job, sometimes 1 for repainting the same color.
• Coverage per Gallon – the area one gallon covers at the recommended film thickness. Most exterior paints cover 250–400 sq ft per gallon, with 350 being a common average.

If you measure in square meters, use the metric coverage (typically 8–12 m² per liter) and convert: 1 gallon = 3.785 liters, 1 sq ft = 0.0929 m².

Worked Example

Using the calculator defaults:

• Wall area = 2,000 sq ft
• Coats = 2
• Coverage = 350 sq ft/gal

Step 1: Multiply area by coats: 2,000 × 2 = 4,000 sq ft of total coverage needed.

Step 2: Divide by coverage per gallon: 4,000 ÷ 350 = 11.4286 gallons.

Rounded to 2 decimals, that’s 11.43 gallons (about 43.3 liters). For primer, one coat over the same area: 2,000 ÷ 350 = 5.71 gallons.

How to Measure Your Exterior Wall Area

Accurate measurements are the foundation of a good estimate. Here’s a simple method:

1. Measure the perimeter of the house (length of all exterior walls) in feet.
2. Multiply perimeter by the height of the walls (from foundation to eaves). For a two-story house, measure each story separately.
3. Subtract the area of large openings: windows (about 15 sq ft each), doors (about 20 sq ft each), and garage doors (about 200 sq ft).
4. Add the area of gables (triangular wall sections under the roof). For each gable, multiply base × height ÷ 2.

For a typical 2,000 sq ft single-story ranch with a 150 ft perimeter and 10 ft walls, the gross wall area is 1,500 sq ft. After subtracting windows and doors, you might get around 1,300 sq ft – quite different from the floor area. Always measure the actual wall surface, not the house footprint.

Factors That Change Coverage

Coverage per gallon is a theoretical number. Real-world conditions can reduce it significantly:

• Surface porosity – bare wood, stucco, and old masonry absorb more paint, sometimes cutting coverage by 20–30%.
• Texture – rough surfaces like brick or textured siding have more surface area than smooth siding, requiring more paint.
• Application method – spraying wastes more paint than brushing or rolling due to overspray and wind.
• Temperature and humidity – painting in hot, dry, or windy conditions causes the paint to dry faster, reducing flow and coverage.
• Color change – going from a dark to a light color (or vice versa) often needs an extra coat.

As a rule of thumb, add 10–15% to the calculated gallons for waste and touch-ups. For rough surfaces, add 20–25%.

Common Mistakes and How to Avoid Them

One frequent error is confusing square footage of floor space with wall area. A 2,000 sq ft house does not have 2,000 sq ft of exterior wall – the wall area depends on the shape and height. Another mistake is forgetting to subtract windows and doors; they add up quickly. Also, don’t round down to the nearest whole gallon – you’ll run short. Always round up to the next full gallon, because paint is sold by the gallon (or 5-gallon pail).

Finally, remember that primer and paint have different coverage rates. Primer often covers less (around 300 sq ft/gal) because it’s designed to seal and absorb into the surface. Use the same formula but with the primer’s coverage number.

Cost Considerations

Paint prices vary widely by brand, quality, and finish. Exterior paint typically costs more than interior because it contains additives for UV resistance and flexibility. A 5-gallon bucket of mid-grade exterior paint might cost anywhere from $100 to $250, while premium lines can be $300 or more. To estimate cost, multiply the gallons by the price per gallon. Don’t forget primer (usually cheaper) and supplies like brushes, rollers, tape, and drop cloths. For a typical 2,000 sq ft house, the paint alone could range from $200 to $600 depending on quality.

Safety and Preparation Tips

Exterior painting involves ladders, scaffolding, and sometimes lead paint in older homes. Always use a sturdy ladder on level ground, have someone spot you, and never overreach. If your house was built before 1978, test for lead paint before sanding or scraping – lead dust is hazardous. Wear a respirator when sanding, and use eye protection. Work in mild weather (50–85°F) and avoid painting in direct sunlight or when rain is forecast within 24 hours. Prepare the surface by cleaning with a power washer, scraping loose paint, and priming bare wood or metal.

Frequently Asked Questions

How many gallons of paint do I need for a 1500 sq ft house exterior?

Assuming 1,500 sq ft of wall area, 2 coats, and 350 sq ft/gal coverage, you’d need about 8.57 gallons, so buy 9 gallons. If you’re painting the trim, add 1–2 gallons more.

Should I use the same calculator for primer?

Yes, but use the primer’s coverage rate, which is often lower (around 300 sq ft/gal). For 2,000 sq ft, one coat of primer would need about 6.7 gallons (round to 7).

Does the type of siding affect how much paint I need?

Absolutely. Smooth hardboard or vinyl siding covers close to the rated amount, while wood shingles, stucco, and brick can require 20–30% more because of texture and porosity.

Is it better to buy 5-gallon buckets or 1-gallon cans?

For large jobs, 5-gallon buckets are usually cheaper per gallon and create less waste. But if you’re using multiple colors, smaller cans are more practical. Always buy a little extra – you can return unopened cans.

How do I convert square meters to square feet for this calculator?

Multiply square meters by 10.764 to get square feet. For example, 200 m² × 10.764 = 2,153 sq ft. Then use the same formula.

What if my walls have a lot of windows and doors?

Subtract their area from the total wall area before calculating. A 2,000 sq ft wall area with 300 sq ft of openings becomes 1,700 sq ft, reducing your paint needs by about 10%.

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in area | Wall area | sq ft | 2000 | 0
in coats | Number of coats | - | 2 | 1
in cover | Coverage per gallon | sq ft/gal | 350 | 50
out gallons | Paint needed | gallons | (area * coats) / cover | 2
out liters | Paint needed | liters | ((area * coats) / cover) * 3.78541 | 1
out primer | Primer needed | gallons | (area * 1) / cover | 2