Standard Fish Tank Dimensions: 10, 20 Long, 29, 40 Breeder, 55 and 75 Gallon

Before you buy a tank, you need to know whether it will fit the space, the stand and the fish you want to keep. Most glass aquariums sold in the US follow a set of standard sizes, so a “55 gallon” from one brand is almost exactly the same footprint as a 55 gallon from another.

This guide lists the standard dimensions of the most popular fish tank sizes in inches and centimetres, explains the difference between look-alike sizes such as the 20 high and 20 long, and gives the approximate filled weight of each so you can plan the stand.

Standard fish tank sizes at a glance

Dimensions are length x width (front to back) x height, measured outside. Real tanks vary by up to about 1/4 inch between brands, so always check the listing for the exact figure before building a cabinet around it.

Tank size	Inches (L x W x H)	Centimetres	Footprint	Approx. filled weight
5 gallon	16 x 8 x 10	41 x 20 x 25	128 sq in	about 60 lb
10 gallon	20 x 10 x 12	51 x 25 x 30	200 sq in	about 116 lb
20 gallon high	24 x 12 x 16	61 x 30 x 41	288 sq in	about 223 lb
20 gallon long	30 x 12 x 12	76 x 30 x 30	360 sq in	about 231 lb
29 gallon	30 x 12 x 18	76 x 30 x 46	360 sq in	about 321 lb
40 gallon breeder	36 x 18 x 16	91 x 46 x 41	648 sq in	about 462 lb
55 gallon	48 x 13 x 21	122 x 33 x 53	624 sq in	about 604 lb
75 gallon	48 x 18 x 21	122 x 46 x 53	864 sq in	about 859 lb
90 gallon	48 x 18 x 24	122 x 46 x 61	864 sq in	about 900 to 1,000 lb
125 gallon	72 x 18 x 21	183 x 46 x 53	1,296 sq in	about 1,389 lb

Filled weights include the water, a typical empty glass tank and a 2 inch gravel bed. See how much a fish tank weighs for the breakdown.

10 gallon fish tank dimensions

A standard 10 gallon tank measures 20 x 10 x 12 inches (about 51 x 25 x 30 cm). Its 20 inch length fits on most desks and dressers, and it holds about 10.4 gallons by outside measurement, or roughly 8 to 9 gallons of water once it is furnished. Filled, it weighs around 116 lb. It is a good size for a betta, a shrimp colony or a small group of nano fish; see how many fish fit in a 10 gallon tank.

20 gallon long dimensions

A 20 gallon long measures 30 x 12 x 12 inches (about 76 x 30 x 30 cm). It holds the same nominal 20 gallons as a 20 high, but spreads it over a longer, lower box. That extra length gives schooling fish more room to swim and bottom dwellers such as corydoras more floor space, which is why many fishkeepers prefer the long version.

20 gallon high dimensions

A 20 gallon high measures 24 x 12 x 16 inches (about 61 x 30 x 41 cm). It takes up less shelf space than the long version and its extra height suits taller plants, but it has 20 percent less floor area than the long version.

29 gallon fish tank dimensions

A 29 gallon tank measures 30 x 12 x 18 inches (about 76 x 30 x 46 cm). It uses exactly the same footprint as a 20 long, just 6 inches taller, which means you can upgrade from a 20 long to a 29 on the same stand if the stand is rated for the extra weight (about 321 lb filled instead of 231 lb).

40 gallon breeder dimensions

A 40 gallon breeder measures 36 x 18 x 16 inches (about 91 x 46 x 41 cm). It is unusually wide and shallow for its volume, which gives it a large surface area for gas exchange and a big floor for bottom dwellers, aquascapes and breeding setups. It is one of the most popular tanks for planted aquariums and for turtles. Do not confuse it with the 40 gallon long (48 x 12 x 16 inches), which is longer but much narrower.

55 gallon fish tank dimensions

A 55 gallon tank measures 48 x 13 x 21 inches (about 122 x 33 x 53 cm). Its 4 foot length makes it a favourite for community fish and long schools, but at only 13 inches front to back it is narrow for large or territorial fish. Filled, it weighs around 604 lb, so it needs a dedicated aquarium stand.

75 gallon fish tank dimensions

A 75 gallon tank measures 48 x 18 x 21 inches (about 122 x 46 x 53 cm). It has the same 4 foot length as a 55 but is 5 inches deeper front to back, which gives fish far more room to turn and makes aquascaping much easier. That depth is why the 75 is a common recommendation for cichlids and larger community fish. Filled, it weighs around 859 lb.

How to measure a tank you already own

If your tank does not have a label, measure the length, width and height on the outside, then compare them with the table above. If two sizes share a footprint, such as the 20 long and the 29, the height tells them apart. To get the exact volume, use the fish tank volume calculator or follow our guide to how many gallons your fish tank holds.

Choosing the right size

• Measure your space first, including the clearance above the tank for the lid, lighting and your arm during maintenance (allow at least 8 to 12 inches).
• Check the stand rating. A filled tank weighs about 10 lb per gallon.
• Buy bigger if you can. Larger volumes are more stable: temperature and water quality change more slowly, which is more forgiving for beginners.
• Match the footprint to the fish. Bottom dwellers and active schools care about length and floor area more than height.

Frequently asked questions

What are the dimensions of a 10 gallon fish tank in cm? About 51 x 25 x 30 cm (20 x 10 x 12 inches).

Is a 20 long or a 20 high better? For most community fish, the 20 long. It has 25 percent more floor area (360 vs 288 square inches) and a longer swimming length.

What is the difference between a 40 breeder and a 40 long? The 40 breeder is 36 x 18 x 16 inches, while the 40 long is 48 x 12 x 16 inches. The breeder is shorter but 6 inches wider, so it has a larger footprint.

Are European tank sizes the same? No. European and Asian tanks are usually sold in centimetres and litres, for example 60 x 30 x 30 cm (54 litres). See the fish tank size chart for common metric sizes.