Gallons per Square Foot Calculator
Estimate paint, stain, or sealant volume from area, spread rate, and coats.
Enter your values and calculate to see the result.
Formula used
area (ft²) = length × width
total gallons = area × coats / coverage
(coverage in ft² per gallon; metric uses m²/L and litres)
litres = gallons × 3.78541
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Worked example
Wall: 20 ft × 10 ft Coverage: 350 ft²/gal Coats: 2
Area: 200 ft² Gallons: (200 × 2) / 350 = 1.14 gal (about 4.32 L)
Buy 2 gallons to have whole containers on hand.
Frequently asked questions
What spread rate should I enter?
Use the number on the product label (square feet one gallon covers). Smooth interior walls run about 350–400 ft²/gal; rough or porous surfaces like bare block or exterior masonry cover far less, often under 250 ft²/gal.
Does the unit toggle change the arithmetic?
No. Switching to metric only relabels the inputs (feet to metres, gallons to litres) and converts your entered numbers in place. The coverage relationship — area times coats divided by spread rate — is identical in either system.
When do I add more coats?
Add a coat whenever you are covering a strong colour with a light one, sealing a porous surface, or applying a primer under a finish. Each extra coat multiplies the volume by one, so two coats need twice the material of one.