Aquarium Volume and Weight Calculator: Gallons and Filled Weight
Work out how many gallons your fish tank holds and how much it weighs filled, from its dimensions, with Aqueon's published tank sizes and empty weights built in.
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A filled fish tank weighs roughly 11 pounds per gallon of its nominal size once you add the glass: Aqueon's chart lists 111 pounds for a filled 10 gallon, 225 for a 20 and 625 for a 55. Water alone is about 8.34 pounds per gallon. The calculator below works out your tank's real water volume from its dimensions and adds the glass, sand and rock to give the weight your stand and floor must carry.
Tank volume and weight calculator
From the maker; Aqueon's figure fills in with a preset.
Weigh the bags you bought or read their labels.
The load the stand's maker rates it for.
Water
19.2 gal
73 litres
Water weight
160 lb
at 8.34 lb a gallon
Filled weight
205 lb
about 78 lb per square foot of footprint
Aqueon prints 225 lb as the filled weight of its 20 gallon Long tank.
Gallons: length x width x water depth in inches, divided by 231 (one US gallon is 231 cubic inches). Fresh water about 8.34 lb a gallon (USGS); salt water is that times the specific gravity you enter. Presets: Aqueon's sizing chart, outside dimensions, so the volume comes out slightly high. Aqueon notes that filled weights vary with substrate and decor.
How it works
- Volume. Length times width times water depth, in inches, divided by 231, because one US gallon is defined as 231 cubic inches. Water depth is the tank height minus the space you leave under the rim.
- Water weight. Fresh water weighs about 62.4 pounds per cubic foot, the USGS says, which works out to about 8.34 pounds per gallon. Specific gravity is the weight of a liquid relative to fresh water, so for salt water the calculator multiplies by the specific gravity you enter (it starts at 1.025, which gives about 8.55 pounds per gallon). Red Sea's salt instructions tell reef keepers to measure it with an accurate hydrometer or refractometer once the water is at 25°C (77°F); use your own reading.
- Filled weight. Water plus the empty tank (Aqueon's figure fills in when you pick a preset) plus whatever you enter for sand, rock, decor and equipment.
- Stand check. If you enter your stand's rated load, the calculator shows the margin or the shortfall.
Aqueon tank sizes built in
| Tank | L x W x H (in) | Empty (lb) | Filled (lb) |
|---|---|---|---|
| 5.5 gallon | 16.19 x 8.38 x 10.5 | 7 | 62 |
| 10 gallon | 20.25 x 10.5 x 12.56 | 11 | 111 |
| 15 gallon | 24.25 x 12.5 x 12.75 | 21 | 170 |
| 20 high | 24.25 x 12.5 x 16.75 | 25 | 225 |
| 20 long | 30.25 x 12.5 x 12.75 | 25 | 225 |
| 29 gallon | 30.25 x 12.5 x 18.75 | 40 | 330 |
| 40 breeder | 36.19 x 18.25 x 16.94 | 58 | 458 |
| 55 gallon | 48.25 x 12.75 x 21 | 78 | 625 |
| 75 gallon | 48.5 x 18.5 x 21.13 | 98 | 785 |
| 90 gallon | 48.5 x 18.5 x 25.13 | 135 | 1,050 |
| 125 gallon | 72.5 x 18.5 x 23.13 | 177 | 1,400 |
Worked examples
| Setup | Water (calculator) | Water weight | Plus tank and extras | Filled |
|---|---|---|---|---|
| 20 long, fresh, 1 in gap, 20 lb sand | 19.2 gal | 160 lb | 25 + 20 lb | about 205 lb |
| 40 breeder, fresh, 1 in gap, 40 lb sand and rock | 45.6 gal | 380 lb | 58 + 40 lb | about 478 lb |
| 55 gallon, fresh, 1 in gap, 50 lb gravel | 53.3 gal | 444 lb | 78 + 50 lb | about 572 lb |
| 75 gallon reef, salt at 1.025, 1 in gap, 80 lb rock and sand | 78.2 gal | 668 lb | 98 + 80 lb | about 846 lb |
The calculator uses outside dimensions, which overstate the water slightly because glass has thickness. Aqueon's filled weights, which include the full tank, sit close to these totals.
Why the weight matters
- The stand. Choose one rated above your filled total. Our stand guide lists each stand's rating against Aqueon's weights.
- The floor. A 75 gallon reef can pass 800 pounds on a footprint of about 6 square feet. For big tanks on upper floors, check with someone qualified about the framing.
- Moving it. Never move a tank with water in it.
Why the volume matters
Heaters, filters, medications and water conditioners are dosed by volume, and the real water volume is usually less than the nominal size. Use the calculator's figure, then subtract a little more for rock and sand. Our heater size calculator takes the volume from here, and our water conditioner guide gives each product's dose per gallon.
More on choosing a tank
See 20 gallon tanks for the 20 long versus 20 high choice, or starter kits for complete setups.
Frequently asked questions
How much does a 55 gallon fish tank weigh?
About 625 pounds filled, according to Aqueon's chart, with 78 pounds of that being the empty tank. Gravel, rock and equipment add more.
How much does a 20 gallon fish tank weigh filled?
About 225 pounds, per Aqueon's chart for both its 20 long and 20 high. The empty tank is 25 pounds of that.
How much does a gallon of water weigh?
About 8.34 pounds for fresh water, from the USGS figure of 62.4 pounds per cubic foot. Salt water weighs that times its specific gravity: at a reading of 1.025, about 8.55 pounds per gallon.
How do I calculate how many gallons my fish tank holds?
Multiply length, width and water depth in inches, then divide by 231, the number of cubic inches in a US gallon. Use the inside measurements and the actual water depth for the most accurate figure.
Does a saltwater tank weigh more than a freshwater tank?
Yes, slightly. Salt water reading 1.025 on a refractometer weighs 2.5 percent more than fresh water, so a 75 gallon reef weighs roughly 15 to 20 pounds more in water alone.
Sources
- Aquarium sizing information (catalog chart), Aqueon
- Water Density, U.S. Geological Survey
- Coral Pro Salt user guide, Red Sea
Cover image: Illustration: Aquarium Gear Review (AI-generated)
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