Gallons Per Square Foot Calculator

A gallons per square foot calculation connects the size of a surface with the published coverage of paint, stain, sealer, waterproofing, fertilizer, or another liquid product. Manufacturers normally state coverage as square feet per gallon. Dividing project area by that rating gives the theoretical gallons needed for one coat. Multiplying by the number of coats extends the estimate to the complete application. This calculator assumes a rectangular surface, so area equals length multiplied by width. The gallons formula is area multiplied by coats, then divided by coverage per gallon. A 20-foot by 20-foot surface has 400 square feet. At 400 square feet per gallon, two coats require two gallons. If you enter a price, the calculator multiplies the unrounded gallon quantity by that unit price to show a material-cost estimate. Published coverage is a planning value rather than a guarantee. Porous concrete, rough masonry, bare wood, textured walls, overspray, roller absorption, and application thickness can all increase consumption. Smooth sealed surfaces may approach the label rating, while first coats on absorbent substrates often cover substantially less. Product instructions take priority because some coatings specify wet-film thickness, dry-film thickness, dilution, or different coverage ranges for different application methods. Measure every surface that will receive material and add their areas before estimating. For walls, calculate each wall separately and subtract doors or windows only when their combined area is meaningful. Irregular areas can be divided into rectangles, calculated independently, and added. Add a sensible waste allowance after obtaining the theoretical result, especially when color matching means leftover material is valuable for future repairs. Purchase sizes matter too: a result of 2.2 gallons generally requires buying three one-gallon cans unless a suitable smaller container is available. The optional cost is for product only. A complete project budget may also include primer, thinner, tools, masking materials, surface preparation, delivery, tax, and labor. Confirm that every dimension uses feet and that the coverage rating is stated in square feet per US gallon. Use the result as a transparent starting point, round the purchase quantity up to available package sizes, and follow the product data sheet for application rate, coat count, drying time, ventilation, and safe handling.