Gallons per Square Foot Calculator
Quickly determine how many gallons of liquid fit in any area at your specified depth. Enter square footage and depth in inches to get exact volume in gallons and liters. Choose your application type for adjusted volume estimates. Works for pools, aquariums, rain barrels, paint jobs, garden irrigation, and industrial tanks.
Total surface area of the space
How deep the liquid sits above the surface
Different applications have slight volume adjustment factors
How many gallons per square foot?
One gallon of water covers approximately 1 square foot at 1.6 inches of depth. More precisely: 1 US gallon = 231 cubic inches. For 1 sq ft (144 sq in) at 1 inch deep: 144 ÷ 231 = 0.624 gallons. At 1/4 inch: 0.156 gallons. At 2 inches: 1.247 gallons. This conversion is critical for pool volume, rainwater collection, aquarium capacity, paint coverage, and irrigation planning.
How many gallons per square foot for paint coverage?
One gallon of paint typically covers 350-400 square feet per coat for smooth surfaces. Rough surfaces (stucco, brick) reduce coverage to 200-250 sq ft per gallon. One gallon per square foot of liquid depth: at 1/8 inch (typical wet film thickness for paint) = 0.078 gallons per sq ft, or about 12.8 sq ft per gallon at that thickness. Primer covers less — about 300 sq ft per gallon.
How do I calculate gallons in a rectangular tank?
Multiply length (ft) × width (ft) × depth (ft) × 7.48052 to get US gallons. For a 4×2 ft tank filled to 1 ft deep: 4 × 2 × 1 × 7.48 = 59.84 gallons. For partial depth in inches: sq ft × (depth in ÷ 12) × 7.48. To find the depth needed for a specific volume: depth (in) = (gallons ÷ 7.48 ÷ area) × 12. This works for any flat-bottomed container or pool.
How many gallons per square foot for a garden?
One inch of water over one square foot = 0.624 gallons. For a 100 sq ft garden bed, 1 inch of water = 62.4 gallons. Most vegetables need 1-1.5 inches of water per week, so plan for 62-94 gallons per 100 sq ft weekly. Drip irrigation uses less — about 0.5 gallons per sq ft per week for established plants. Use these numbers to size rain barrels or irrigation timers.