What Size Tank Do Hermit Crabs Need? (Tank Size Chart)
Hermit crabs need about 5 gallons of tank space per small crab, and more for bigger ones. A 20-gallon tank is the realistic starting point for a small group.
The pet store may tell you a small plastic carrier is fine. It is not, and the reason is not just floor space.
How Much Space Does a Hermit Crab Need?
Use this simple rule:
- Small and medium crabs: about 5 gallons each
- Large crabs: about 10 gallons each
- Jumbo crabs (over 3 inches across): about 15 gallons each
Hermit crabs are social, so keep at least 3 together. That is why 20 gallons, not 10, is the real starting point. Here is why hermit crabs should not live alone.
More space is always better. A tank that looks big from outside fills up fast once you add sand and water dishes.
Hermit Crab Tank Size Chart:
These are comfort limits, not maximums. Fewer crabs in a bigger tank is always healthier.
| Tank size | Small or medium crabs | Large crabs | Jumbo crabs |
|---|---|---|---|
| 10 gallon | 2 (starter only) | 1 | Not suitable |
| 20 gallon | 3 to 4 | 2 | 1 |
| 29 gallon | 4 to 5 | 2 to 3 | 1 to 2 |
| 40 gallon | 6 to 8 | 4 | 2 to 3 |
| 55 gallon | 8 to 10 | 5 | 3 |
| 75+ gallon | 10 or more | 6 to 7 | 4 to 5 |
Most owners do best with a 20 to 29 gallon tank. It fits a healthy group and holds humidity well.
Why Tank Size Matters For Hermit Crabs:
Deep Substrate:
Crabs need at least 6 inches of damp sand and coconut fiber to molt safely. Jumbo crabs need 10 to 12 inches.
In a 10-gallon tank, 6 inches of sand leaves very little room above it.
Molting Caves
Each crab digs its own cave to molt. If two crabs dig in a small tank, they can break into each other’s cave.
A disturbed molting crab can die.
Water Dishes
Crabs need two dishes, fresh and salt, deep enough to soak in. In a small tank, they take up a big share of the floor. See how to make salt water for hermit crabs.
Climbing and Hiding
Hermit crabs are active at night. They need things to climb and places to hide, or they get stressed and fight over shells. Good tank mates and decor keep them busy.
The 10-Gallon Reality Check:
A 10-gallon tank technically works for two small crabs as a starter. But after sand, two water dishes, food, and spare shells, there is almost no space left.
Your crabs will outgrow it fast. If you can only buy one tank, buy the biggest one that fits your space.
Used tanks from Facebook Marketplace or Craigslist are often much cheaper. They do not even need to be watertight, since hermit crabs live on land.
Why Bigger Tanks Are Easier For Hermit Crabs:
Big tanks change slowly. Small tanks lose heat and humidity fast, and those swings stress crabs.
There is one catch. A bigger tank needs a stronger heater, wider water dishes, and a sealed lid to hold 70 to 80 percent humidity.
Size alone does not make a tank easier. Deep sand, a tight lid, and good heat do.
Wide Tank or Tall Tank?
Go wide. Floor space matters more than height, because the bottom 6 inches are filled with sand.
A little height is still good for climbing, so a long, wide tank with some height is ideal.
Plan for Them to Grow:
Hermit crabs grow slowly for their whole life, and they can live 15 to 25 years.
A crab that fits in your palm today could reach baseball size in five to ten years. Buy the tank for the size they will be, not the size they are now.
What to Put in Hermit Crab Tank:
Once you have the right size, you need a few basics:
- Glass tank with a tight lid. Skip wire or mesh tops, they let humidity escape.
- At least 6 inches of substrate. Play sand and coconut fiber, about 5 parts sand to 1 part fiber.
- Two water dishes. One fresh, one marine salt, both dechlorinated.
- A side-mounted heat mat with a thermostat. Never under the tank. See our guide on heating a hermit crab tank.
- Spare shells and hides. 3 to 5 spare shells per crab, plus driftwood and hiding spots. Here is why hermit crabs need shells.
Conclusion:
Plan for about 5 gallons per small crab, 10 per large crab, and 15 per jumbo. For a group of 3, a 20-gallon tank is the real starting point, and 29 gallons gives them room to grow.
Go wide, add deep sand, and hold the heat and humidity steady. A little extra space now saves a lot of stress later.
(FAQs):
A: Only as a short-term starter for 2 small crabs. Upgrade to 20 gallons as they grow.
A: Three to four small or medium crabs, or two large ones.
A: At least 3. They are social and get stressed when kept alone.
A: Wide is better. Floor space matters more than height because the bottom is filled with sand.
A: Sand. Gravel and rocks block digging and can hurt them.
