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🐚 Shell Fit Calculator
Ideal Opening Size
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Opening
* Visual size is relative representation
Enter size to see results
Hermit Crab Shell Fit Guide
Finding the correct shell size is crucial for your hermit crab’s health. A shell that is too small can cause suffocation or drying out, while a shell that is too big can be too heavy to drag around, leading to lethargy.
How to Measure
To use the calculator above, you need to estimate the size of your crab. There are two common methods:
- Big Claw Method: Measure the height of the large claw (cheliped) when the crab is tucked in or resting.
- Shield Width (Precise): Measure the width of the hard part of the back (carapace) just behind the eyes.
Pro Tip: Always offer 3-5 shells per crab in your tank to prevent fighting (“shell aggression”).
Understanding Opening Shapes
Different species prefer different opening shapes:
- Round (Turbo): Preferred by Purple Pinchers (PPs). Look for Green Turbos, Mexican Turbos, or Petholatus shells.
- D-Shaped: Preferred by Ecuadorians. Look for Babylonia or Whale Eye shells.
- Oval/Slit: Some exotic species prefer slit openings, though these are less common in the pet trade.
Why Shell Scarcity Matters
In the wild, hermit crabs fight to the death for good shells. In captivity, shell scarcity is a massive stressor. By providing a variety of appropriately sized shells calculated above, you significantly reduce stress and aggression in your colony.