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How Big Can Hermit Crabs Get? Size Chart & FAQs

Sarah Psaradelis

By Sarah Psaradelis

white spotted hermit crab in shell walking along sand in tank aquarium

Hermit crabs are low-maintenance pets with the ability to live for up to 20 years. They are often sold as inexpensive pets that are ideal for children and the whole family. As a crustacean that grows differently from us, you might not know how big they can grow or even how these creatures grow.

The size of the hermit crab will influence the size of the enclosure, making it important to know how big you should expect your hermit crab to grow before you get them. Even if you have already gotten a hermit crab, it is still fascinating to learn how big they can get, and the answer might surprise you! The biggest hermit crab can grow up to 8 inches and weight of 8 ounces!

Adult Hermit Crab Sizes

Here are the most common pet hermit crabs and how big each one grows:

Type: Size: Weight:
Strawberry Hermit Crab (Coenobita perlatus) 3.5 to 6 inches 2.8 to 4 ounces
Australian Land Hermit Crab (Coenobita variabilis) 1.6 to 2 inches 1.3 ounces
Blueberry Hermit Crab (Coenobita purpureus) 2 inches 1.5 ounces
Passionfruit Hermit Crab (Coenobita cavipes) 1.5 to 4 inches 1.5 to 2.8 ounces
Ecuadorian Hermit Crab (Coenobita compressus) 0.5 inches 1 ounce
Indonesian Hermit Crab (Coenobita brevimanus) 8 inches 8 ounces
Ruggie Hermit Crab (Coenobita rugosus) 2 to 2.5 inches 1.5 to 2.5 ounces
Caribbean Hermit Crab (Coenobita cylpeatus) 3 to 6 inches 2.8 to 4 ounces

The size of the hermit crab will depend on the type you are keeping. There are around 1,100 different species of hermit crabs, but only a few species are kept as pets. It is not uncommon for male hermit crabs to grow larger than females.

Some hermit crabs such as the strawberry and Caribbean hermit crab can grow as large as 6 inches, while others hardly grow larger than an inch in size like the Ecuadorian hermit crab.

When it comes to the largest species of terrestrial hermit crab, the coconut hermit crab (Birgus latro) grows to 40 inches in size and weighs up to 9 pounds. However, the coconut hermit crab is not kept as a common pet, and they are instead found in the wild on various islands such as the Caroline and Gambier Islands.

The smallest territorial hermit crab is the Ecuadorian hermit crab, which doesn’t get much larger than 0.5 inches in size. While the largest marine or saltwater hermit crab that lives in an aquatic environment is the giant red hermit crab (Pterochirus diogenes) which reaches a size of 12 inches.

The small marine dwarf zebra hermit crab (Calcinus laevimanus) doesn’t get much larger than an inch, making them one of the smallest hermit crabs in the ocean.

hermit crabs out of their shells, hermit crabs closeup
Image Credit: Kurit afshen, Shutterstock

How Do Hermit Crabs Grow?

Hermit crabs have a unique way of growing since they are a crustacean, and they gain size and weight by molting. They will shed their old exoskeleton through a molting cycle that consists of four different stages: the proecydsis, ecdysis, metacdysis, and anecdysis stage.

The old exoskeleton may look like your hermit crab, but it is instead an empty exoskeleton. Soon after your hermit crab molts, their new exoskeleton will begin to harden, and they will go back to their usual behaviors.

At first, it might seem like your hermit crab is dead. A molting hermit crab will stop moving, but it is important to leave a hermit crab alone when they are molting, as interfering with a hermit crab’s molt can do more harm than good. The entire molting process may take anywhere from 2 to 8 weeks long, depending on the size and species of hermit crab.

During this time, the hermit crab will require a bigger shell so you will need to provide them with slightly larger shells each time they molt and grow. Molting will happen more frequently when they are in their juvenile stage, and once the hermit crab has grown to an adult size, the molting will slow down.

Older hermit crabs may only molt every 18 to 20 months, and they will not stop molting for the rest of their lives. Once the hermit crab has undergone a molt, they will likely consume the old exoskeleton for extra nutrients, so don’t take it away from them too quickly.

How Fast Do Hermit Crabs Grow?

It can take years for a hermit crab to reach their adult size, and with such a lengthy lifespan, many hermit crabs don’t make it to their adult size due to early death. Most hermit crabs have a lifespan of 10 to 20 years, with some species known to live till 30 years of age.

Hermit crabs will reach adult size at around 2 to 3 years of age, but some hermit crabs can take several years before reaching their final size due to an improper diet and poor living conditions, or they are simply a very large species of hermit crab that will take longer to grow.

hermit crab on sand
Image By: EllenChan, Pixabay

What Size Enclosure Do Hermit Crabs Need?

A hermit crab’s environment should replicate one that is similar to their wild habitats, as this will allow the hermit crab to feel more comfortable and display their normal behaviors.

The size of the enclosure will depend on the species, but a 20-gallon-long aquarium is a good starter size for most hermit crabs.

Some species such as the Caribbean or Strawberry hermit crab need a bigger enclosure since they can grow to 6 inches. Some smaller species such as the Ecuadorian hermit crab can be kept in a tank as small as 10 gallons, but if you plan to keep a large group of them, you will need to increase the tank size accordingly.


Hermit crabs in captivity don’t typically grow larger than 8 inches in size, with many species only reaching around 1 to 2 inches. The size of the hermit crab will depend on the species, which will influence their enclosure size and overall appearance.

When properly cared for, hermit crabs can be a long commitment and live for one or two decades. During the years you will be able to watch the hermit crabs grow until adulthood when they reach their final size, which can be quite fun to experience.

Featured Image Credit: Zuzha, Shutterstock

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