40-gallon Breeder Tank Dimensions and Guidelines

40-gallon Breeder Tank Dimensions

Pet fish owners might want to take it to the next level and start raising and breeding their own fish. If this sounds like something that interests you, then you’ll have to invest in a handy spawning or breeder tank.

As far as breeder tanks go, you’ll find that they come in various sizes—from tiny 2.5-gallon tanks to massive 225-gallon aquariums that pro breeders use. But the most widely used breeder tank size, at least among greenhorn fish breeders, is the 40-gallon variety.

The measurements of the tank differ between manufacturers. From a technical standpoint, the tank should hold 9,240 cubic inches of water, but you’ll most likely come across 40-gallon breeder tanks measuring 36 × 18 × 16 inches (10,368 cubic inches).

An Introduction to Breeder Tanks

An Introduction to Breeder Tanks

At first glance, newbies and laypeople may have trouble distinguishing breeders from typical fish tanks.

In short, it’s a type of aquarium used to promote breeding. It is more “squashed” than regular fish tanks, giving you a better view and access to your stock. Most breeder tanks stand 16 inches tall, thus making it longer and narrower than the typical aquarium. The exact measurements of a breeder tank, even a single size like a 40-gallon tank, will differ between brands.

When comparing similarly sized fish tanks and breeder tanks, the only difference is the shape. Both types of tanks will hold identical amounts of water, but breeder tanks have a larger surface area due to their low profile and length.

40-Gallon Breeder Tank Dimensions

A 40-gallon breeder tank, which fish-raising hobbyists refer to simply as a 40 breeder, will typically stand 16 inches tall. However, the precise measurements will vary based on what company made the tank.

There are 3 common size options when it comes to 40-gallon breeders and 1 less commonly used size option. These options are known as 40 high, 40 long, 40 breeder, and 40 cube, which have only slight differences in terms of the total size.

  • A 40 high tank averages 36 × 13 × 20 inches (9,360 cubic inches)
  • A 40 long tank averages 48 × 12 × 16 inches (9,216 cubic inches)
  • A 40 breeder tank, which is considered the standard, averages 36 × 18 × 16 inches (10,368 cubic inches)
  • A 40 cube tank will measure 20.75 inches in all sizes (8,934.2 cubic inches)

Of the 4 size options mentioned above, the 40 long and 40 cube tanks cannot technically be classified as 40-gallon breeder tanks since they are about 24 cubic inches and 305.8 cubic inches shy of holding 40 gallons of water, respectively.

Buying a 40-Gallon Breeder Tank

Before settling on a particular 40-gallon breeder tank model, there are several points you need to consider.

Why Are You Getting a 40-Gallon Breeder Tank?

The first question you mask ask yourself is why you want to get a 40 breeder. Do you plan on raising only one species of fish or a diverse community? Your answer will dictate the size of the tank you end up purchasing.

Before even considering the tank type and size, you should have a good understanding of how to set up your tank based on fish species. To demonstrate, aggressive fish species need a larger place to move around and claim territory as their own, whereas more docile species can thrive in large communities and in relatively smaller tanks.

How Much Are You Going to Spend on a 40-Gallon Breeder Tank?

You should expect to spend anywhere from $150 to $500 on a 40 breeder, but some of the more top-notch ones can run for upwards of 2 grand.

But purchasing is only the capital expense. You will also have to consider additional equipment, which can add up to around $200, as well as operating expenses of around $20 monthly. On top of that, there’s also the cost of fish feed and heating of around $15 per month.

On average, you may end up spending around $35 to $40 every month.

FAQ About Breeder Tanks

1. Should I get a 40-gallon breeder tank or a 50-gallon breeder tank?

How large or small the tank is should depend on the type and number of fish you want to raise. Predatory fish require more space (larger tanks) to move and claim a spot in the tank as their own, whereas docile fish can thrive in a community and in relatively smaller tanks. You may get by with a smaller 10- to 20-gallon tank if you’re just starting off, but a 40-gallon tank will allow you to be more flexible in your experimentation.

2. How many guppies can I keep in a 40-gallon breeder tank?

In general, a single guppy will need 1 gallon to survive. You may get by with 40 guppies in a 40-gallon tank, though some people have pushed the limits to 100 guppies per 40 gallons of water and succeeded. Your first step before becoming a hobbyist breeder is to research each fish species to determine how large or small a breeder tank to go with.

3. Can you breed fish in a regular tank?

Yes, you can. In fact, people may have accidentally done so when they purchased 2 fish of the opposite genders and the same species. The reason breeder tanks are better for intentionally breeding fish is that they have a wider surface area, giving the owner an unobstructed view of what’s going on underwater. Decorated tanks may make it more difficult for breeders to see what’s going on in there.


A 40 breeder averages around 36 × 18 × 16 inches, but the size variety will play a role in how long, wide, and tall the tank is. Before settling on a particular tank model, make sure you put in the research before transitioning from pet owner to hobbyist breeder.

If you found this article helpful, please make sure you share it on your socials. If you’re a seasoned fish breeder, I’d love to hear about your experience working with 40-gallon breeder tanks.


Baron Cooke has been writing and editing for 7 years. He grew up with an aptitude for geometry, statistics, and dimensions. He has a BA in construction management and also has studied civil infrastructure, engineering, and measurements. He is the head writer of measuringknowhow.com

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