10, 20, and ...29???...Gallon Aquariums

Aquariums are a bit of a hobby of mine, and have been since I was a kid. I’m thinking about buying a 29-gallon tank, and I have to ask–why 29 gallons and not 30? I’ve always assumed it had to do with shape and design of the tank, but then again, one more gallon isn’t much. Anyone have any other ideas? (Or better…anyone know the answer?)

Typical tank sizes are 5, 10, 20, 29, 40, 55, 60, 75, 100, and 220 (largest non-custom available). I’ve also wondered–why have a 55 and and 60 gallon tank? When you’re dealing with two 4ft tanks, what marketable difference does an extra 5 gallons make?

“Me fail English? That’s unpossible!”

“English? Who needs that? I’m never going to England.”

The difference really is the size and shape. The sizes designate a particular arrangement. For example the 29 gallon tank is a tall tank, and the less popular 30 looks like a blown up 10 (much wider and much more depth from the back glass to the front without being very tall. The 29 doesn’t actually hold 29 gallons, it’s less but close enough. If you look at the different sizes (like 55 and 60) you will find different configurations. In the last 15 years or so they have also added the “show” designation to certain configurations. The 29 would be a “show” tank being nice from the outside but a little narrow for some larger fish.

If I remember correctly, there are several tank sizes (20-long, and the 29) which have a greater ‘floor space’ ratio than the normal tank. If you’ve got lizards or snakes or tarantulas or something, you’d be more concerned about the floor space that’s available than the total volume of the tank.


I need to make one correction, LauraRae. I worked in a fish store for 3 years during high school (7 years ago) and the largest non custom size aquariums we stocked were 225 gallons. Also you missed some sizes in your list. 90, 115, 125, 140, 150. These last sizes were more of the longer tanks which provided more surface area for the amount of water, except the 140 and 90. These were the tall varaties. The 90 was really a tall 55.

As if the aquarium sizes aren’t confusing enough, I’d like to point out that they’re not even accurate. If you measure the inside volume of your aquarium (or the outside volume and correct for the glass thickness) and then multiply it by 7.48 gallons per cubic foot, you’ll find that the liquid volumes are off by a bit. A fifty five gallon tank, for example, holds closer to fifty gallons. If you figure on gravel and an air gap at the top of the tank, it’s more like forty five. This is a minor point but it’s worth remembering when adding medications and other chemicals to your tank.