Exterior Paint Calculator: Square Feet Coverage

This exterior paint calculator works out how much paint you need for a house or building exterior. You enter the total wall area in square feet, the number of coats, and the paint’s coverage rate (square feet per gallon), and it returns the estimated gallons required. It also shows the total square feet you’ll actually cover, accounting for the number of coats.

Formula

The formula used is straightforward:

Paint needed (gallons) = Wall area (sq ft) × Number of coats ÷ Coverage rate (sq ft per gallon)

Variables:

• Wall area – the total exterior surface you plan to paint, in square feet. This includes walls, gables, and any other flat surfaces, but excludes windows, doors, and other openings.
• Number of coats – how many layers of paint you’ll apply. Most exterior jobs need at least 2 coats for even color and durability.
• Coverage rate – the area one gallon of paint covers, in square feet. This is usually printed on the paint can and varies by brand and surface texture (typically 250–400 sq ft per gallon).

Worked Example

Using the default values from the calculator: wall area = 1500 sq ft, coats = 2, coverage = 350 sq ft/gal.

1. Total area to cover = 1500 × 2 = 3000 sq ft
2. Paint needed = 3000 ÷ 350 = 8.57 gallons

Since paint is sold in whole gallons, you’d round up to 9 gallons. The calculator shows 8.6 gallons (rounded to one decimal), which is the exact amount; you’ll need to buy 9 gallons for the job.

How to Measure Your Exterior Wall Area

To get an accurate estimate, you need the square footage of the surfaces you’ll paint. Here’s a practical method:

• Measure the perimeter of the house (length of all exterior walls) in feet.
• Multiply the perimeter by the average wall height (usually 8–10 ft for a single-story home). This gives the total wall area including windows and doors.
• Subtract the area of openings: for each window, multiply width × height; for each door, multiply width × height. Add them all and subtract from the total.
• Add gable areas: for each triangular gable, multiply base × height ÷ 2.

For a typical 2,000 sq ft single-story home with a perimeter of 180 ft and 9 ft walls, the gross wall area is 1,620 sq ft. After subtracting about 200 sq ft for windows and doors, you get roughly 1,420 sq ft of paintable surface.

Why Coverage Rate Varies

The coverage rate on the paint can is an ideal number based on smooth, primed, and non-porous surfaces. Real-world coverage is often lower due to:

• Surface texture – stucco, brick, or rough wood absorb more paint than smooth siding.
• Porosity – bare wood or old, chalky paint soaks up more than a primed surface.
• Application method – sprayers use more paint than rollers or brushes due to overspray.
• Weather conditions – hot, dry, or windy days cause paint to dry faster, reducing spread.

For rough or porous surfaces, reduce the coverage rate by 20–30%. For example, if the can says 350 sq ft/gal, use 250–280 sq ft/gal for stucco.

Common Mistakes and How to Avoid Them

• Forgetting to subtract openings – including windows and doors in the wall area overestimates paint by 10–15%.
• Ignoring the number of coats – a single coat rarely covers well; always multiply by the actual number of coats you’ll apply.
• Rounding down – always round up to the nearest gallon. Running out of paint mid-job means color mismatch if you buy more later.
• Mixing units – if you measure in meters, convert to feet before using this calculator (1 meter = 3.28084 feet).
• Not accounting for trim and soffits – if you’re painting trim, fascia, or soffits a different color, measure those separately and add their area to the total.

How to Read the Result

The result is the exact number of gallons needed for the specified area and coats. Since paint is sold in whole gallons (and sometimes quarts), you’ll need to round up to the nearest whole gallon. For a 1,500 sq ft house with 2 coats, you’d need 9 gallons. If you’re painting a different color for trim, buy an additional 1–2 gallons for trim and doors, depending on their size.

It’s also wise to buy 10% extra paint for touch-ups and future repairs. For the example above, that means buying 10 gallons instead of 9.

Limitations of This Calculator

This calculator gives a good estimate, but it can’t account for every variable. It assumes a uniform surface and even application. Actual paint usage can be higher if:

• The surface is very rough or heavily weathered.
• You’re painting a dark color over light, requiring extra coats.
• You’re using a sprayer, which wastes 10–20% of paint.
• The paint is of lower quality with lower solids content.

For a final quote, always consult the paint manufacturer’s data sheet and, ideally, a professional painter’s estimate.

Frequently Asked Questions

How many square feet does a gallon of exterior paint cover?

Typically, one gallon of exterior paint covers 250–400 square feet per coat, with 350 sq ft being a common average for smooth, primed surfaces. Rough surfaces like stucco or brick reduce coverage to 200–250 sq ft per gallon.

How much exterior paint do I need for a 2000 square foot house?

Assuming a single-story home with 9-foot walls and average window/door area, the wall area might be around 1,500–1,800 sq ft. With 2 coats and 350 sq ft/gal coverage, you’d need about 9–11 gallons for the walls, plus extra for trim.

Should I use the same coverage rate for primer?

No. Primer typically covers less than paint, often 200–300 sq ft per gallon, because it’s designed to seal and absorb into the surface. Check the primer can for its specific coverage rate and calculate separately.

How many coats of exterior paint do I need?

Most exterior paint jobs require at least 2 coats for even color and durability. If you’re painting over a similar color and the surface is in good condition, one coat might suffice, but two is safer for hiding imperfections and extending the life of the paint.

Does the calculator work for metric measurements?

No, it uses square feet and gallons. If you measure in meters, convert to feet first (1 m = 3.28084 ft). For liters, note that 1 US gallon = 3.78541 liters, so multiply the gallons result by 3.785 to get liters.

What if I’m painting brick or stucco?

For rough, porous surfaces, reduce the coverage rate by 20–30%. For example, use 250 sq ft/gal instead of 350. This will increase the estimated gallons, which is more realistic for these materials.

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in area | Wall area | sq ft | 1500 | 0
in coats | Coats | - | 2 | 1
in coverage | Paint coverage | sq ft/gal | 350 | 1
out gallons | Paint needed | gallons | area * coats / coverage | 1
out total_area | Total area to cover | sq ft | area * coats | 0