How Much Does a Full Fish Tank Weigh?

Before you set up a new aquarium, it is worth knowing how much it will weigh when full. Water is surprisingly heavy, and a large tank can stress a stand or even a floor. The good news is that the weight is easy to work out once you know the volume.

The simple rule

Fresh water weighs almost exactly 1 kilogram per litre. In imperial units, a US gallon of water weighs about 3.79 kilograms, or 8.34 pounds. So the filled weight of your tank is roughly your water volume in litres, in kilograms, plus the weight of the tank itself.

How to calculate the full weight

1. Find the water volume. Use the fish tank volume calculator to get the volume in litres.
2. Convert litres to water weight. Multiply litres by 1 kg. A 200 litre tank holds about 200 kg of water.
3. Add the empty tank, stand, substrate and rocks. Glass and substrate add a meaningful amount, often 15 to 30 percent more.

Worked example

A 120 by 50 by 60 cm tank holds 360 litres. The water alone weighs about 360 kg. Add roughly 60 to 90 kg for the glass, substrate and decor, and the loaded weight is well over 400 kg. That is a lot to place on a single piece of furniture.

Check your stand and floor

Always use a stand rated for the full loaded weight, and place large tanks against a load-bearing wall where possible. A spirit level helps you confirm the stand is even, which spreads the load and reduces stress on the glass seams.

Saltwater is slightly heavier

Salt water is a little denser than fresh water, at about 1.025 kg per litre. For a reef tank, add around 2 to 3 percent to the fresh water figure, then include live rock and sand on top.

Knowing the weight in advance keeps your setup safe and your floor intact.