Gallons to liters & aquarium water weight

Convert US gallons, liters, Imperial gallons and cubic feet, and estimate how much the water in your aquarium weighs.

Formulas

• Liters = US gallons × 3.785411784; Imperial gallons = liters ÷ 4.54609; cubic feet = liters ÷ 28.316846592.
• Water weight (kg) = liters × density (g/cm³) × specific gravity. Pounds = kg × 2.20462.

Fresh water is a little lighter when warm. USGS lists 0.99802 g/cm³ at 70 °F and 0.99669 g/cm³ at 80 °F, so 55 US gallons (208.2 L) of 80 °F fresh water weighs about 457 lb (207.5 kg). For salt water, enter the specific gravity from your hydrometer or refractometer.

Why weight matters

The water is only part of the load. Glass, the stand, substrate and rock add more, so check the manufacturer’s ratings for your stand and floor. This page doesn’t give structural advice; ask a qualified professional if you’re unsure.

Sources

• NIST Special Publication 811, Appendix B.8 (conversion factors)
• USGS Water Science School, “Water Density”

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