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How Many Hermit Crabs Can You Keep Per Gallon In An Aquarium?

With the popularity of keeping hermit crabs constantly increasing due to a number of videos on social media of pet hermit crabs going viral, we have noticed a spike in the number of people reaching out with various questions about keeping their own pet hermit grab.

One of the more common questions that we have seen people asking is about how many hermit crabs they can keep per gallon of their tank.

As there is such a high number of people reaching out and asking questions about how many hermit crabs they can keep per gallon of their tank, we wanted to publish our own dedicated article going over the topic.

Keeping hermit crabs is not as straight forward as keeping some other popular animals as there are over 800 different species of hermit crab with some being aquatic and some being terrestrial.

This means that the number of hermit crabs you can keep per gallon of your tank will depend on the specific species of your hermit crab as well as if it is aquatic and kept in an aquarium of it it is terrestrial and kept in a vivarium.

On top of that, some hermit crab species can be more aggressive than others so they tend to need more free space per hermit crab than other species too making things even more complicated.

How Do You Workout How Many Hermit Crabs You Can Keep Per Gallon?

There are two general rules for working out how many hermit crabs you can keep in your tank with the first being one permit crab per 2.5 gallons of tank capacity and this being the more commonly used one due to being so simple.

The second method is to make sure that your pet hermit crabs have at least one gallon of tank per one inch of hermit crab size with this method being more accurate but taking longer to work out.

We know that the majority of people who keep hermit crabs tend to just go with the first method as it is so much easier to work with when stocking your aquarium or vivarium with hermit crabs but it can sometimes result in problems.

This is due to some hermit crab species being around half an inch in size when fully grown to others being as large as four inches in length when fully grown to using the two and a half gallon pet hermit crab is never totally accurate.

It can be a pain to work out the size of your hermit crabs and you don’t have to use exact measurements but the second method of trying to estimate the size of the grab to allocate set gallons to it in your tank is the better option.

We would always recommend that our readers try to go with the second method if possible as it is more accurate and helps you prevent any accidently overstocking of your tanks when getting your hermit crabs.

“Hermit Crab” by GraveBone is licensed under CC BY-NC 2.0. To view a copy of this license, visit

How Many Hermit Crabs Can You Keep Per Gallon In An Aquarium?

If you are keeping a small hermit crab species then you may be able to get away with one of even two hermit crabs per gallon of your aquarium but larger hermit crab species will usually need as much as four gallons in your aquarium.

For example, a ten gallon tank could have two large hermit crabs in it taking up eight gallons with two gallons being spare of that same tank can have ten smaller hermit crabs taking up one gallon each.

You also have to factor in the type of tank you have and we would always recommend against using any tall tanks due to hermit crabs usually being on your substrate rather than swimming around. In our opinion, a cheap 10 gallon long tank is the perfect option for anyone looking to get into keeping hermit crabs.

Longer tanks are always better than tall tanks for all types of crabs and the tank can then be turned into an aquarium or vivarium as needed depending on the species of hermit crab you keep.

Although that ten gallon tank can technically keep as many as twenty half inch hermit crab species or ten one inch hermit crab species, we would not recommend it.

Just because you are able to stock your tank to those levels does not mean that you should and most people tend to workout the maximum stocking capability of their tank and then half it.

Does Overstocking Your Hermit Crabs Cause Problems In The Tank?

Accidently adding too many hermit crabs to your tank can result in aggression, especially with terrestrial hermit crab species as they are territorial and will fight for space.

Aquatic hermit crab species are usually more placid towards each other but they can sometimes see your fish as food and will try to catch your fish and eat them unless you have a large tank that is understocked.

As we covered in our article going over if hermit crabs eat each other or not, there are some situations where hermit crabs will eat each other too so it is generally better to try and understock your tank leaving plenty of space rather than to risk overstocking it.

This is why so many people who do keep hermit crabs as pets will work out the maximum number of hermit crabs per gallon they are able to keep in their tanks and then half this number.

If you are brand new to keeping hermit crabs then we would highly recommend that you implement this rule too until you have built up some experience of caring for hermit crabs.

Although they may look cute and innocent on social media, some hermit crabs, especially the terrestrial land hermit crab species can be surprisingly aggressive with fights being common if their tank is overstocked.


That brings our article going over how many hermit crabs you can keep per gallon of your aquarium to an end. We hope that we have been able to help you better understand how many hermit crabs you should be looking to keep in your tank no matter its size as the calculations we have shared earlier in the article really do make it quick and easy to workout the maximum number of crabs you can keep. Ideally though, you should be looking to half that number to make sure that there is plenty of space available for your crab in their tank.