Gallons per Square Foot Calculator

For a standard 12x12 room with 8-foot ceilings, you need to calculate the wall area. Four walls would measure 12 × 8 × 4 = 384 square feet. Subtracting for a standard door (20 sq ft) and window (15 sq ft), you'd have about 350 square feet to paint. At an average coverage of 350 sq ft/gallon, you would need about 1 gallon. However, for two coats, plan on 2 gallons. For the ceiling (144 sq ft), you'd need about 0.5 gallons more.

Coverage rates can vary significantly based on application method, surface porosity and texture, environmental conditions, and application technique. Rough, porous surfaces like bare wood or brick absorb more product than smooth, sealed surfaces. Additionally, darker colors may require more coats to achieve full coverage, and thinner applications may require multiple coats. Always use the product label as a starting point, but adjust based on your specific conditions.

For irregular shapes, break the area down into basic geometric shapes (rectangles, triangles, circles), calculate the area of each, and then add them together. For example, a room with an alcove can be calculated as a rectangle plus another smaller rectangle. Once you have the total square footage, divide by the coverage rate to determine how many gallons you need.

Yes, it's recommended to add 10-15% extra to your calculated amount to account for spillage, waste, uneven application, and touch-ups. For complex projects with many corners, trim areas, or detailed work, you might want to add up to 20% extra. It's always better to have a little left over than to run short in the middle of a project, especially if you're using a custom-mixed color that might be difficult to match exactly.

For multiple coats, multiply your calculated gallons by the number of coats you plan to apply. For example, if your project requires 2 gallons for one coat and you plan to apply two coats, you'll need 4 gallons total. However, note that second coats often require less product than first coats, especially on previously painted or sealed surfaces, so you might use 10-20% less for subsequent coats.

For a standard two-car garage floor (approximately 400-500 square feet), with epoxy coverage typically being 100-200 square feet per gallon, you would need about 2-5 gallons of epoxy, depending on the specific product and how many coats you plan to apply. Most epoxy floor applications require a primer coat and at least one topcoat, so plan accordingly. Also consider that rough or porous concrete will require more product than smooth, sealed concrete.