10 Gallon Fish Tank Dimensions

A typical 10 gallon fish tank is 20.25 inches long, 10.50 inches wide, and 12.56 inches high on the outside. That is the Aqueon 10 gallon leader from the company's 2023 critical-dimensions sheet. The rounded size people repeat, 20 x 10 x 12 inches, is a close description of the same tank, not a second official size.

Tank	Length (in)	Width (in)	Height (in)	Rated gal	Outside box (gal)	Empty lb	Full lb
2.5 gallon	12.19	6.13	8.13	2.5	2.63	2.6	27
5.5 gallon	16.19	8.38	10.50	5.5	6.16	7	62
10 gallon	20.25	10.50	12.56	10	11.56	11	111
15 gallon	24.25	12.50	12.75	15	16.73	21	170
20 gallon high	24.25	12.50	16.75	20	21.98	25	225
20 gallon long	30.25	12.50	12.75	20	20.87	25	225
29 gallon	30.25	12.50	18.75	29	30.69	40	330
40 gallon breeder	36.19	18.25	16.94	40	48.42	58	458
55 gallon	48.25	12.75	21.00	55	55.93	78	625
75 gallon	48.50	18.50	21.13	75	82.05	98	785
90 gallon	48.50	18.50	25.13	90	97.59	135	1050
125 gallon	72.50	18.50	23.13	125	134.27	177	1400

Outside length, width, and height, empty weight, and full weight are from Aqueon's 2023 critical dimensions sheet. Outside box gallons equal those three inches multiplied, then divided by 231. That column is not the water volume. Full weight varies with substrate and decor. Source: Aqueon critical dimensions (PDF).

10 gallon fish tank length

Length is the long side: 20.25 inches outside. Width is the front-to-back depth, 10.50 inches. Height is 12.56 inches. If you only have room for a 20 inch opening, measure the stand, not the water, and use 20.25 inches plus a little clearance for hoses and the frame.

If the water itself measures 20 x 10 x 12 inches, the volume is 20 x 10 x 12 / 231 = 10.39 US gallons. Calculate 20 x 10 x 12. The rated 10 gallons is lower because the outside box is not the water.

20, 29, 55, and 75 gallon dimensions

The 20 gallon long is 30.25 x 12.50 x 12.75 inches outside. The 20 gallon high is 24.25 x 12.50 x 16.75. The 29 gallon is 30.25 x 12.50 x 18.75, so it shares the 20-long footprint and adds height. The 55 gallon is 48.25 inches long and only 12.75 inches front to back, which is why it fits a narrow stand and gives fish a long swim. The 75 gallon is 48.50 x 18.50 x 21.13, the same family of length with a much deeper front-to-back.

30 x 12 x 12 and 36 x 18 x 18

Those two sizes show up as "how many gallons" questions, and they are internal water questions, not rows in this outside chart. 30 x 12 x 12 inches of water is 18.70 US gallons. 36 x 18 x 18 inches of water is 50.49 US gallons. An older catalog approximated a 50 gallon as 36 x 18 x 18. Use the volume calculator for any size you measured yourself.

Weight on the stand

Aqueon's full weights already include a filled tank. The 10 gallon full weight in the sheet is 111 lb. The 55 gallon is 625 lb. The 75 gallon is 785 lb. Put the tank on a stand built for aquariums, and check that the floor can take the load. The volume page also shows a rough 10 lb per gallon planning figure for water plus gravel and decor.

Frequently asked questions

How long is a 10 gallon fish tank?

The Aqueon 10 gallon leader is 20.25 inches long on the outside, 10.50 inches wide, and 12.56 inches high. People often round that to 20 x 10 x 12. Those rounded inches, if they were the water, equal 10.39 US gallons.

What are the dimensions of a 20 gallon long?

Aqueon's 20 gallon long is 30.25 inches long, 12.50 inches wide, and 12.75 inches high on the outside. The 20 gallon high is 24.25 x 12.50 x 16.75. Same rated gallons, different footprint.

Why is the outside box more gallons than the rated size?

The published length, width, and height include the frame and the glass. Dividing that box by 231 counts plastic and glass as if they were water, and it assumes the tank is filled to the top edge. The rated gallon is the manufacturer's water capacity, which is smaller.

How do I get the real water volume?

Measure the water with a tape and use the aquarium volume calculator. Do not type the outside chart into that calculator and expect the rated gallons to come back.