🐟 Fish Tank Size Calculator
Calculate your aquarium volume in gallons & liters — supports rectangle, cylinder, bow front & more shapes
| Tank Name | Dimensions (L x W x H in) | Volume (gal) | Volume (L) | Water Weight (lbs) |
|---|---|---|---|---|
| 2.5 Gal Desktop | 12 x 6 x 8 | 2.5 | 9.5 | 20.9 |
| 5 Gal Nano / Betta | 16 x 8 x 10 | 5 | 18.9 | 41.7 |
| 10 Gal Starter | 20 x 10 x 12 | 10 | 37.9 | 83.4 |
| 15 Gal | 24 x 12 x 12 | 15 | 56.8 | 125.1 |
| 20 Gal High | 24 x 12 x 16 | 20 | 75.7 | 166.8 |
| 20 Gal Long | 30 x 12 x 12 | 20 | 75.7 | 166.8 |
| 29 Gal Community | 30 x 12 x 18 | 29 | 109.8 | 241.9 |
| 40 Gal Breeder | 36 x 18 x 16 | 40 | 151.4 | 333.6 |
| 55 Gal Standard | 48 x 13 x 21 | 55 | 208.2 | 458.6 |
| 75 Gal | 48 x 18 x 21 | 75 | 283.9 | 625.1 |
| 90 Gal | 48 x 18 x 24 | 90 | 340.7 | 750.1 |
| 125 Gal | 72 x 18 x 22 | 125 | 473.2 | 1041.9 |
| 180 Gal | 72 x 24 x 25 | 180 | 681.4 | 1500.2 |
| US Gallons | Liters | UK Gallons | Cu. Inches | Cu. Feet | Water Weight (lbs) |
|---|---|---|---|---|---|
| 1 | 3.785 | 0.833 | 231 | 0.134 | 8.34 |
| 5 | 18.93 | 4.16 | 1,155 | 0.668 | 41.7 |
| 10 | 37.85 | 8.33 | 2,310 | 1.337 | 83.4 |
| 20 | 75.71 | 16.65 | 4,620 | 2.674 | 166.8 |
| 50 | 189.27 | 41.63 | 11,550 | 6.684 | 417.0 |
| 100 | 378.54 | 83.27 | 23,100 | 13.37 | 834.1 |
| Tank Volume | Water Weight | Filter GPH Min | Heater Watts | CO2 (planted, bps) |
|---|---|---|---|---|
| 5 gal / 19 L | 42 lbs / 19 kg | 25 GPH | 25 W | 0.5–1 bps |
| 10 gal / 38 L | 83 lbs / 38 kg | 50 GPH | 50 W | 1 bps |
| 20 gal / 76 L | 167 lbs / 76 kg | 100 GPH | 75 W | 1–2 bps |
| 29 gal / 110 L | 242 lbs / 110 kg | 145 GPH | 100 W | 1.5–2 bps |
| 55 gal / 208 L | 459 lbs / 208 kg | 275 GPH | 200 W | 2–3 bps |
| 75 gal / 284 L | 625 lbs / 284 kg | 375 GPH | 250 W | 3–4 bps |
| 125 gal / 473 L | 1042 lbs / 473 kg | 625 GPH | 400 W | 4–5 bps |
Your actual usable water volume is always less than the tank's gross capacity. Subtract 5–15% for substrate, decorations, and fill level. Use the calculator's adjustment sliders for an accurate result.
Water weighs 8.34 lbs per US gallon (1 kg per liter). A 55-gallon tank holds roughly 459 lbs of water alone — always verify your stand and floor can support the total weight including the tank and substrate.
Choosing the right Size for a Fish Tank is harder than many think. Likely you already heard about that old rule of one gallon each inch that seems easy on paper. But here the problem: fish of 11 inches will not need the same space as one of 10 inches.
That guideline is only a good starting spot, and real research about the needs of your particular fish always pays the effort.
How to Choose the Right Fish Tank Size
Fish Tank setups offer seemingly endless choices. On the little end, one finds tanks between 2.5 and 10 gallons. For medium setups the amounts sit between 15 and 30 gallons.
When one reaches the big range, sizes go from 50 to 75 gallons. More than that? Here one enters the area of tanks at 400 or even 800 gallons.
At such Size, everything becomes truly serious.
For beginners, a setup of 20 gallons commonly is the best choice. A long tank of 20 gallons is especially good, because it delivers more horizontal space for your fish than a tall model with same content. Here why that matters: a tank with low height gives bigger surface area, what directly helps oxygen stay in the water.
With 20 gallons you can easily keep a school of little fish like tetras or rasboras, or maybe a pair of territorial species like dwarf cichlids.
Generally, a bigger tank is always better. One commonly calls 30 gallons the lowest limit for a setup that stays quite a lot steady without need of constant changes. When your space and money allows, choose the biggest possible, especially for saltwater tanks.
For starting a saltwater aquarium, amounts around 55 to 75 gallons work well, where 75 gallons form a solid start for saltwaer tanks.
Goldfish show clearly why the Size of a Fish Tank is so important. Those little goldfish in pet stores are only each one inch or a bit more, but they grow surprisingly quickly and can reach 12 inches easily. A tank that seems perfect at first soon becomes too narrow.
I learnt that a 40 gallon breeder tank best works four a pair of fancy goldfish.
The form and measures of a tank matter almost as much as the gallon number. A long 20 gallon and standard 30 gallon can have the same floor area, but the 30 gallon stores around 50 percent more water, so more room, more fish. Generally wider and longer beats tall.
A column tall tank does not work, because the depth can stop oxygen and light spreading well. A standard 55 gallon? It has only around 12 inches of depth in front, what makes decorating and hiding spots truly hard.
Different makers give a bit different measures for same gallon amount, and sometimes it depends even on the color. Take a flexible tape with you to the fish store. Truly, it saved me many times when I mixed marks for covers and stands.
Renters certainly must check how big a Fish Tank their home allows, because big tanks risk bigger water damage if something breaks. And heavytanks need strong furniture below, because the weight grows quickly.
