What Is a Gallon per Square Foot?
A gallon per square foot is not a standard unit of volume — it is a derived measure that combines area (square feet) and depth to produce a volume in gallons. To find how many gallons fit in a given area, you also need to know the depth (height) of the liquid or material.
What Is a Gallon?
There are three types of gallons in common use:
- US gallon — 3.785411784 liters (231 cubic inches). Symbol: US gal.
- UK (Imperial) gallon — 4.54609 liters (8 pints). Symbol: UK gal.
- US dry gallon — ⅛ of a US bushel (≈ 4.405 liters). Rarely used outside agriculture.
This calculator uses the US gallon and the UK gallon.
How Many Gallons in One Cubic Foot?
There are exactly 7.48052 US gallons in one cubic foot. For UK gallons, one cubic foot equals 6.22884 UK gallons.
This means: if you have a surface of area A ft² covered to a depth of H feet, the volume in US gallons is:
Volume (US gal) = A (ft²) × H (ft) × 7.48052
How Many Gallons per Square Foot?
Since 1 ft³ = 7.48052 US gal, and 1 ft³ = 1 ft² × 1 ft depth:
US gal per ft² = depth (ft) × 7.48052
For example, at a depth of 1 inch (= 0.0833 ft):
0.0833 × 7.48052 ≈ 0.6234 US gal per ft²
How to Use This Calculator
- Choose your unit system: US Imperial (sq ft, inches) or Metric (m², cm).
- Choose the direction: Area → Volume, or Volume → Area.
- For Area → Volume: enter the surface area and the depth of water or liquid. The calculator returns the volume in US gallons, UK gallons, liters, and cubic feet.
- For Volume → Area: enter the volume (in US gal, UK gal, or liters) and the depth. The calculator tells you the area this volume covers.
Practical Examples
Swimming pool
A rectangular pool 20 ft × 40 ft (= 800 ft²) with a uniform depth of 5 ft:
Volume = 800 × 5 × 7.48052 ≈ 29,922 US gallons
Aquarium
An aquarium base of 4 ft² filled to a depth of 1.5 ft:
Volume = 4 × 1.5 × 7.48052 ≈ 44.88 US gallons
Irrigation pond (metric)
A pond 100 m² at 0.5 m deep:
Volume = 100 × 0.5 = 50 m³ = 13,208 US gallons
Key Conversion Factors
| From | To | Factor |
|---|---|---|
| 1 ft³ | US gallons | 7.48052 |
| 1 ft³ | UK gallons | 6.22884 |
| 1 ft³ | Liters | 28.3168 |
| 1 US gal | Liters | 3.78541 |
| 1 UK gal | Liters | 4.54609 |
| 1 m² | ft² | 10.7639 |
| 1 ft² | m² | 0.092903 |
FAQs
Can I convert square feet to gallons without knowing the depth?
No. Area (ft²) is two-dimensional; gallons measure three-dimensional volume. You always need depth to make the conversion.
What is 1 gallon per square foot?
1 US gallon per ft² corresponds to a depth of 1 ÷ 7.48052 ≈ 0.1337 ft (about 1.6 inches).
How do I convert gallons to square feet?
Divide the volume in cubic feet by the depth in feet:
Area (ft²) = Volume (ft³) / Depth (ft) Volume (ft³) = Gallons (US) × 0.133681
US gallon vs UK gallon — which should I use?
If you are in the United States (or Canada for some purposes), use the US gallon. If you are in the United Kingdom or another country that follows the imperial system, use the UK gallon. The UK gallon is about 20% larger than the US gallon.