Understanding Gallons Per Square Foot
Gallons per square foot is a measurement that relates a liquid volume to the surface area it covers. This metric is widely used in construction and landscaping for estimating how much paint, sealant, epoxy, stain, or water is needed to cover or treat a given surface area at a specific thickness or application rate.
One US gallon equals 231 cubic inches, or approximately 0.1337 cubic feet. When spread uniformly over one square foot at one inch of depth, one gallon covers approximately 1.6 square feet. Understanding this relationship helps contractors order accurate quantities and avoid costly waste or shortages.
Conversion Formula
Simplified:
Coverage Rates by Material
| Material | Coverage per Gallon | Typical Thickness |
|---|---|---|
| Interior Paint | 350 – 400 sq ft | ~4 mils (0.004") |
| Exterior Paint | 250 – 350 sq ft | ~5 mils |
| Epoxy Coating | 100 – 200 sq ft | ~10–20 mils |
| Deck Stain | 150 – 300 sq ft | ~3–5 mils |
| Concrete Sealer | 200 – 300 sq ft | ~2–4 mils |
| Waterproofing | 50 – 100 sq ft | ~30–60 mils |
Worked Example
Applying a 1-inch layer of water over 1,000 square feet:
Frequently Asked Questions
How many gallons of paint do I need per square foot?
One gallon of interior paint covers about 350-400 square feet per coat, which equals approximately 0.0025 to 0.003 gallons per square foot per coat. Two coats double that amount.
How do I calculate gallons for a pool cover?
Multiply the pool surface area in square feet by the average depth in feet, then multiply by 7.481 to convert cubic feet to gallons. A 15x30 ft pool at 5 ft average depth holds about 15 x 30 x 5 x 7.481 = 16,832 gallons.
What is the difference between wet mils and dry mils?
Wet mil thickness is the thickness of the coating immediately after application. Dry mil thickness is after the solvents evaporate. Dry thickness is typically 40-60% of wet thickness, depending on the solids content of the coating.
How much water is 1 inch of rain per square foot?
One inch of rain on one square foot equals 144 cubic inches, or about 0.623 gallons. Over 1,000 square feet (a small roof), that is 623 gallons of water from a single inch of rain.