A standard 55 gallon tank holds 208 litres, weighs 625 lb when it is full of water according to Aqueon, and needs about a 275 W heater and a filter that moves 220 gallons an hour. Pick your size in the calculator and the same five numbers appear for it, with the load your floor takes under the tank and a table of every common size.
How the numbers are worked out
Volume is the rated gallons the maker prints on the tank, converted at 3.785 litres to a gallon. Weight is the maker's own filled figure from Aqueon's dimensions sheet (10 to 125 gallons) and the Marineland listing for the 180. Those figures are for water only, with no gravel, decor or stand. The floor load divides the filled weight by the outside footprint: 625 lb over 48.25 × 12.75 inches, or 4.27 square feet, is 146 lb per square foot.
Heater (W) = gallons × 5 W up to 55 gallons, × 3 W above. Filter flow (gph) = gallons × turnovers per hour
Heater size
Aqueon's rule of thumb is 5 watts per gallon for tanks of 55 gallons or smaller and 3 watts per gallon above 60 gallons, and more in a cold room, against an outside wall or by a door. For the 55 gallon that is 275 W, and for the 125 gallon 375 W. AquariumScience.org argues for a ceiling of 3 watts per gallon in total, split over two heaters, because a heater that sticks on can raise the water 30 to 50 degrees Fahrenheit. For the 55 that is 165 W in two heaters, which is enough in a room that stays near 70°F. The calculator shows Aqueon's figure and the cautious total.
Filter size
Filtration turnover means how many times an hour the filter moves the whole tank volume. LiveAquaria says on average you turn the aquarium over four times an hour, and MarineAndReef.com recommends 3 to 4 times for filtration in any aquarium, with up to 10 times for freshwater species that like a strong current. At 4 times a 55 gallon needs 220 gallons an hour, 833 litres an hour. The rating on a filter is measured at zero head height, so real flow after media, tubing and lift is lower, and you should buy a filter rated above the number.
Standard tank sizes
| Tank | Outside size (inches) | Litres | Filled weight | Heater | Flow at 4x |
|---|---|---|---|---|---|
| 10 gallon | 20¼ × 10½ × 12 9/16 | 38 | 111 lb | 50 W | 40 gph |
| 20 gallon high | 24¼ × 12½ × 16¾ | 76 | 225 lb | 100 W | 80 gph |
| 20 gallon long | 30¼ × 12½ × 12¾ | 76 | 225 lb | 100 W | 80 gph |
| 29 gallon | 30¼ × 12½ × 18¾ | 110 | 330 lb | 145 W | 116 gph |
| 40 gallon breeder | 36 3/16 × 18¼ × 16 15/16 | 151 | 458 lb | 200 W | 160 gph |
| 55 gallon | 48¼ × 12¾ × 21 | 208 | 625 lb | 275 W | 220 gph |
| 75 gallon | 48½ × 18½ × 21 1/8 | 284 | 785 lb | 225 W | 300 gph |
| 90 gallon | 48½ × 18½ × 25 1/8 | 341 | 1,050 lb | 270 W | 360 gph |
| 125 gallon | 72½ × 18½ × 23 1/8 | 473 | 1,400 lb | 375 W | 500 gph |
| 180 gallon | 72 × 24 × 24 | 681 | 1,788 lb | 540 W | 720 gph |
Sizes are Aqueon's, except the 180 from Marineland. Other brands differ by a fraction of an inch. Makers weigh the tank full to the rim, which is why the 125 gallon reads 1,400 lb: its outside box works out to about 134 gallons. The heater column drops from the 55 to the 75 because the rule changes from 5 to 3 watts per gallon above 55 gallons.
How heavy is a fish tank
The weights in the table are water plus glass. Add gravel (see the aquarium substrate calculator), rock, a stand and a hood, and use the aquarium volume calculator for the filled weight of your exact tank. Reef Builders quotes typical floors at 40 lb per square foot on the ground floor and 30 upstairs, as averages over the room. Every tank in the table puts more than that on its own footprint, so place it over a wall and across the joists, and check with an engineer before installing a big tank above the ground floor.
How many fish can I keep
Gallons alone do not answer that: species, adult size and the filter matter. The aquarium stocking calculator works from your tank and filter. For a saltwater tank you also need the mix for the salinity calculator. The full set of tank tools is on the aquarium hub.