Stocking your fish tank, especially for the first time, can be very exciting, but, you need to be sensible about it.

When adding fish to your tank, it is very important to keep your tank at least slightly understocked. Having too many fish will lead to illness, fighting and even death.

One of the biggest mistakes that people make with tropical fish is overcrowding their tank.

**As a general rule, the calculation for how many fish can go into your tank is 1 inch of adult fish per 1 gallon of water, making sure to take 10% of water off for gravel, decorations etc. Territorial species of fish will need double the space, so 1 inch of fish per 2 gallons of water.**

However, this is just a general rule. There are other things to take into consideration, which I will cover later on.

**Things to Consider When Calculating How Many Fish.**

**Water Measurement.**

Depending on where in the world you are, your tank capacity will either be in gallons or litres.

In America, they use US gallons. A US gallon is different to an imperial gallon (just to complicate matters even more). 1 imperial gallon is the same as 1.2 US gallons.

In the UK, they use litres. 1 litre is the same as 0.3 US gallons, or 0.2 imperial gallons.

**There is a BIG difference between a litre and a gallon when it comes to the size of a fish tank. 1 litre is the equivalent of 0.3 US gallons.**

**Substrate, Plants and Decorations.**

As a general rule, you should take away at least 10% of the water in your calculation to account for any gravel, plants and ornaments. If you have many plants in your tank, I would up that to 15%, just to be on the safe side.

**Single Species or Community Tank?**

It is slightly more difficult to calculate space requirements if you have a community tank as some species of fish can be territorial so need double the amount of space.

Do your research on the different types of fish you would like to see what their temperament is like.

**Size.**

This is probably the most important thing to remember. You must do your calculations based on the **adult size of your fish**, not the size they are when you get them.

Again, do your research to find out what the average adult size of your fish species will grow to before working out how many you can add to your tank.

**Future Proofing.**

When a Mummy fish and a Daddy fish love each other, they make many baby fish! If you are going to have males and females of the same species, you will end up with more fish. If you have stocked your tank up fully your tank will get very overcrowded very quickly once this starts happening.

**How Many Killifish Can I Put into a Tank?**

When it comes to adding Killifish to your tank, there a few things you need to consider.

Killifish are mostly peaceful and social folk, although a few can be aggressive towards their own species. Always make sure to do your research beforehand.

In addition to having the correct sized tank for your Killifish, you also need to make sure you have the correct shape. Killifish need loads of space to swim around the middle and top of the tank, so need a large surface area to be able to do so. It is no good having a really tall but narrow tank as this will not give them the space they need. You will also need a lid on your tank as these guys are jumpers!

It is easy to work out the surface area of a tank.

Surface area of a fish tank = length x width.

**To calculate how many fish you can have using this method is:**

**1 inch of adult fish for every 12 square inches of water surface area. For wide bodied fish, it is 1 inch of adult fish for every 20 square inches.**

**The greater the surface area of** **your tank, the more fish you should be able to have.**

If your calculations don’t end up as a whole number, always round your number down to err on the side of caution.

There is a brilliant fish stocking calculator website, called aqadvisor.com where you can put in your tank dimensions, the type of filter you have, and what type of fish you want to add. This will calculate what percentage stocked you will be, as well as advise you about water change amounts and frequencies. I have found this calculator to be the most accurate and informative.

**Related Posts:**

**How Many Rasboras Can Fit in a Tank?**

**How Many Danios Can Fit in a Tank?**

**How Many Tetras Can Fit in a Tank?**

**How Many Killifish Can Fit in a 40, 60, 75 or 125 Gallon Tank?**

The vast majority of Killifish are classed as narrow bodied fish.

For the purpose of the table I have compiled, I have taken 3 different sized species of Killifish:

**The Clown Killifish,** adult size 2 inches approx. Other examples of Killifish that grow to the same size are:

Red Lyretail, Walker’s Aphyosemion Killifish, Twin-banded Killifish.

**The Lyretail Killifish,** adult size 3 inches approx. Other examples of Killifish that grow to this size are:

Steelblue Killifish, Blue Panchax.

**The Red Aphyosemion,** adult size 5 inches approx. Other examples of Killifish that grow to this size are:

Six-banded Killifish.

I have compiled information for both gallons and litres.

I would use these tables as a rule of thumb rather than Gospel. This is what I would do if stocking my own tank. I would always suggest you double check with aqadvisor.com to be doubly certain.

**Don’t forget, the figures in the tables below, are only for if you are not adding any other species of fish to your tank.**

**Killifish Calculator in Gallons.**

**How Many Killifish Will Fit in a 60, 80, 100 or 140 Litre Tank?**

**Killifish Calculator in Litres**

Litre | Minus 10% | Clown Killifish (2 inch) | Lyretail Killifish (3 inch) | Red Aphyosemion (5 inch) |
---|---|---|---|---|

25 | 22 | 2 | 1 | – |

60 | 54 | 6 | 3 | 2 |

70 | 63 | 7 | 4 | 2 |

80 | 72 | 8 | 5 | 3 |

100 | 90 | 10 | 6 | 3 |

140 | 126 | 14 | 7 | 4 |