Aquarium Size Chart
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Aquarium sizes are sold under names like a 20-gallon long or a 55-gallon that hide real differences in footprint, filled weight, and how many fish the tank can comfortably support, and mixing up a tall tank with a long one of similar volume can leave you short on the floor space or swimming room your stocking plan assumed. This chart lists common US tank sizes in gallons and liters alongside typical dimensions and filled weight.
Common tank sizes: gallons, liters, and dimensions
10 gallon (38 liters): approximately 20 x 10 x 12 inches (51 x 25 x 30cm), filled weight around 111 pounds (50kg). The standard entry-level tank size, small enough for a desk or shelf.
20 gallon long (76 liters): approximately 30 x 12 x 12 inches (76 x 30 x 30cm), filled weight around 225 pounds (102kg). The long, low footprint gives more swimming and floor space than a standard 20 gallon high of the same volume.
29 gallon (110 liters): approximately 30 x 12 x 18 inches (76 x 30 x 46cm), filled weight around 330 pounds (150kg). A popular step-up size offering meaningfully more stocking room than a 20 gallon.
40 gallon breeder (151 liters): approximately 36 x 18 x 17 inches (91 x 46 x 43cm), filled weight around 458 pounds (208kg). The wide, shallow footprint is popular for planted tanks and bottom-dwelling species since it maximizes floor area relative to volume.
55 gallon (208 liters): approximately 48 x 13 x 21 inches (122 x 33 x 53cm), filled weight around 625 pounds (283kg). A common mid-size community tank that needs a purpose-built stand due to its weight.
75 gallon (284 liters): approximately 48 x 18 x 21 inches (122 x 46 x 53cm), filled weight around 850 pounds (386kg). A substantial tank requiring serious floor loading consideration and a sturdy, level stand.
Filled weight and floor loading
Water alone weighs about 8.34 pounds per US gallon (1kg per liter), and the total filled weight, including the tank, substrate, and decor, typically runs 10-15 percent higher than the water weight alone, which is why a 55 gallon tank's filled weight lands well above 55 times 8.34. Always place a tank over 20 gallons on a stand rated specifically for aquarium use rather than ordinary furniture, and check with a builder or landlord before placing large tanks in upper-floor apartments, since concentrated point loads from a stand's legs can matter more than the average weight per square foot suggests.
A completely full tank is never actually moved full; always drain a tank substantially before relocating it even a short distance, since the combination of water weight and glass stress makes moving a filled aquarium a genuine breakage and injury risk.
General stocking guidelines by tank size
The old rule of one inch of fish per gallon is a rough starting point at best and breaks down badly for larger, more active, or more waste-producing fish, so treat it as a floor rather than an accurate ceiling for stocking any tank. Bioload, how much waste a fish produces relative to its size and activity level, filtration capacity, and adult size (not the size at purchase) all matter more than a simple length-to-volume ratio, which is why two tanks of identical gallon size can support very different stocking plans depending on what is actually kept in them.
A more reliable approach for beginners is to research the specific adult size, activity level, and social needs of each species before stocking, use an online stocking calculator that accounts for bioload rather than length alone, and stock gradually while monitoring water parameters, since overstocking a newly cycled tank is one of the most common causes of preventable fish loss in the hobby.