The first thing you need to consider when you are trying to determine how many hermit crabs you can house is tank size. This is a factor. If you have the minimum 10-gallon aquarium, you are most certainly not going to be able to house as many hermit crabs as a person with a 150-gallon aquarium. The small hermit crab kit cages are most certainly not adequate for one hermit crab to live in comfortably, let alone more than one. A 10-gallon aquarium is the smallest recommended to house a single crab and be able to expand your crab habitat somewhat.
Another thing you must take into consideration when deciding how many hermit crabs you want to buy is the fact that, while hermit crabs are social creatures, they must be able to roam around in their own personal space. Many pet stores have an appropriately sized aquarium for a few hermit crabs, but they have the audacity to jam it full where the hermit crabs are forced to live on top of each other. This is an unacceptable situation for anyone to have, but especially pet stores that are supposed to be humanely housing their stock of animals. You have to take into account if each of your hermit crabs will have enough room to go off on their own for a little while. Each crabbie should be able to have some alone time now and then.
Another thing to consider is that, if you are a keeper of hermit crabs for any length of time, you will inevitably run into a crab that must go through the molting process. You need to make sure that in your hermit crab habitat, there is plenty of room for a safe molting haven. If the hermit crabs do not have the space to molt, they can not molt safely, away from other hermit crabs. Also take into account that if you have quite a few hermit crabs, more than one crab may molt at the same time. You must allow for this. Another thing to think about is whether or not you want a variety of different size crabs.
One last thing to consider when making sure to purchase a home big enough for the amount of hermit crabs you want to buy is to consider the furnishings that must go into the tank with the hermit crabs. Remember, you will have food and water bowls, climbing toys, shelters and other decorations in your tank. In order for your hermit crabs to live comfortably around these things, you must take this into consideration as well. You also want to make sure the hermit crabs have space to take a run as well as the space to maneuver between objects without getting stuck. One more aspect of spacing the furniture is that you need to keep things in the central part of your hermit crab habitat. If you set items near the edge of the habitat, hermit crabs are more prone to escape.
Though there is no set number of hermit crabs per gallon like goldfish have, the biggest thing to remember is to use your best judgment and common sense. Don’t allow the hermit crabs to be so crowded that they cannot maneuver around each other or their furnishings. Make sure everyone has a spot to call their own. Just keep the comfort of your hermit crabs in mind when deciding on the number you can care for.