What this calculator works out
This calculator multiplies length, width and water depth to give a tank's volume in litres.
Use water depth rather than tank height. A tank filled to within a few centimetres of the rim holds noticeably less than its stated capacity, and the difference matters for dosing.
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Before you use the figure
- Measure internal dimensions where you can. Glass thickness reduces the volume by a litre or two on a small tank.
- Water depth is to the actual water line, not the top of the glass.
- Substrate, rocks and decor displace water — commonly 10% or more of the gross volume in a planted tank.
- A litre of water weighs a kilogram. The volume figure is also the weight figure, before glass, stand and contents.
63 litres is 63 kg of water, plus perhaps 20 kg of glass, substrate and decor. On a small footprint that is a substantial point load, and the Can My Floor Take It? calculation applies directly. Aquariums are among the heaviest things people put on an upstairs floor without thinking about it.
How this calculator works
Three dimensions multiplied and converted:
Litres = length × width × water depth ÷ 1,000
All dimensions in centimetresDividing by 1,000 converts cubic centimetres to litres. For dosing purposes the net volume — after substrate and decor — is what matters, and deducting 10 to 15% from the gross figure is a reasonable working assumption.
Worked example: a 60 cm tank
Using the default figures — 60 by 30 cm with 35 cm of water:
- Volume: 63 litres
63 litres is also 63 kg of water. Add glass, a stand, substrate and rocks and the whole assembly is comfortably over 90 kg on a footprint of 0.18 m² — which is around 500 kg per square metre, more than three times the design figure for an upper floor. Position matters more than total weight, and against a wall running at right angles to the joists is where it should go.
Common mistakes
- Using tank height instead of water depth. They differ by several centimetres.
- Dosing to gross volume. Substrate and decor displace 10% or more.
- Forgetting the weight. Water is a kilogram a litre and the tank is a concentrated load.
- Using external dimensions on a small tank. Glass thickness matters proportionally more.
- Filling to the rim. Leave room for displacement and evaporation.
Frequently asked questions
How much does an aquarium weigh?
The water alone is one kilogram per litre. Add roughly 15 to 25% for glass on a typical tank, plus substrate at around 1.5 kg per litre of gravel or sand, plus rocks and the stand. A 100 litre tank set up is commonly 140 to 160 kg, concentrated on a small area.
Where should I put a tank?
On a level floor, against a load-bearing wall, ideally running at right angles to the joists so the load spreads across several. Away from direct sunlight, which drives algae growth, and away from radiators and draughts. Anything above about 60 litres upstairs is worth checking properly rather than assuming.
Why does net volume matter?
Because medications, water conditioners and fertilisers are dosed per litre. Dosing a 63 litre tank as though it held 63 litres when substrate and rocks reduce it to 55 gives a 15% overdose — which for most treatments is tolerable and for some is not. Working from the net figure is the safer habit.
Is what I enter stored?
No. Measurements are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — Approved Document A on structure and floor loading, and animal welfare law
- RSPCA — guidance on the welfare needs of fish kept in aquariums
Sources are checked at publication and can change — how I choose and check references.