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How the calculation works
Water mass equals actual liters × density in kg/L. Freshwater at around 25°C is approximately 0.997 kg/L; saltwater has a different density. Enter a suitable measured or trusted density rather than treating every gallon as a universal water weight.
Add the empty tank, substrate, rock and decor, equipment, cabinet and any other load that the supporting surface carries. Use consistent dry or installed component masses and avoid counting the same water twice. Actual water should already exclude solid displacement, while the solid substrate and rocks are added as their own masses.
The sum is a mass estimate. It cannot assess floor joists, point loading, stand construction, levelness, anchors, earthquakes or the distribution of force. An acceptable tank weight depends on the particular structure and installation. This calculator gives no structural certification, safety rating or maximum permitted aquarium size.
Worked example
100 liters of water at 0.997 kg/L contributes 99.7 kg. Add a 20 kg tank, 10 kg substrate, 5 kg rock and 3 kg equipment for an estimated total of 137.7 kg, about 303.58 lb. Add cabinet mass if it is not already included.
Common questions
Does this prove my floor or stand can hold the aquarium?
No. Load-bearing decisions require information about the actual supporting structure. Use manufacturer stand ratings and qualified structural advice where needed.
Should I include the cabinet?
Include it when evaluating the load on a floor. When assessing a stand’s aquarium rating, follow the stand maker’s scope and avoid double counting.