Answer
How much does a fish tank weigh when full?
Fresh water weighs about 8.34 lb per US gallon, so a 55-gallon tank holds about 451 lb of water when filled an inch below the rim; with glass, gravel, rock and stand, plan for well over 500 lb.
Water weight by tank size
| Tank | Size (in) | Water weight |
|---|---|---|
| 5.5 gallon | 16 × 8 × 10 | 42 lb (19 kg) |
| 10 gallon | 20 × 10 × 12 | 79 lb (36 kg) |
| 15 gallon | 24 × 12 × 12 | 114 lb (52 kg) |
| 20 high | 24 × 12 × 16 | 156 lb (71 kg) |
| 20 long | 30 × 12 × 12 | 143 lb (65 kg) |
| 29 gallon | 30 × 12 × 18 | 221 lb (100 kg) |
| 40 breeder | 36 × 18 × 16 | 351 lb (159 kg) |
| 55 gallon | 48 × 13 × 21 | 451 lb (204 kg) |
| 75 gallon | 48 × 18 × 21 | 624 lb (283 kg) |
| 90 gallon | 48 × 18 × 24 | 717 lb (325 kg) |
| 125 gallon | 72 × 18 × 21 | 936 lb (424 kg) |
Can my floor hold it?
Big tanks put a lot of weight on a small footprint. Put large tanks on a ground floor or across floor joists, and ask a builder if you’re unsure.
More questions
How much does gravel add?
Substrate is heavy: a few inches across a large tank can add tens of pounds.
Is saltwater heavier?
Slightly: seawater is about 2 to 3% denser than fresh water.
How much does a 20-gallon tank weigh full?
The water alone is about 143 lb; with glass and gravel plan for well over 200 lb.
How much does a 75-gallon tank weigh?
About 624 lb of water, before glass, stand and substrate.
How much does a 125-gallon tank weigh?
About 936 lb of water alone.
Can I put a big aquarium upstairs?
Big tanks concentrate weight; place them across floor joists or on a ground floor, and ask a builder if unsure.
How much does water weigh per gallon?
About 8.34 lb per US gallon of fresh water.
Does the stand need to be special?
Yes, use a stand rated for the tank’s full weight.
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Sources
- 8.34 lb per US gallon of fresh water; volumes from standard tank dimensions.