UseCalcPro
Home
MathFinanceHealthConstructionAutoPetsGardenCraftsFood & BrewingTools
Blog
  1. Home
  2. Pets

Hermit Crab Habitat Calculator

Calculate the ideal crabitat for your hermit crabs

Tank Size

29-gallon

Volume

23 gal

Substrate

6" deep

Hermit crabs are social; keep 3+ together

Recommended Habitat

29-gallon

23 gallons minimum

Substrate

6" deep

23 qt

Extra Shells

12

Habitat Requirements

Temperature75\u201385\u00B0F
Humidity70\u201380%
Water Dishes2 (fresh + salt)
Climbing Items2

Substrate Mix

5:1 Ratio

Mix 5 parts play sand with 1 part coconut fiber. Must hold shape when squeezed (sandcastle consistency).

Molting Zone

Deep substrate is critical. Crabs bury to molt and can stay underground for weeks.

What You'll Need

Fluval 307 Performance Canister Filter

Fluval 307 Performance Canister Filter

$120-$1604.6
View on Amazon

Saltwater Master Test Kit 550-Test with Sea Salt

$48-$554.5
View on Amazon
HITOP 100W Adjustable Aquarium Heater Submersible

HITOP 100W Adjustable Aquarium Heater Submersible

$12-$184.3
View on Amazon
Fluval 307 Performance Canister Filter

Fluval 307 Performance Canister Filter

$120-$1604.6
View on Amazon

Saltwater Master Test Kit 550-Test with Sea Salt

$48-$554.5
View on Amazon
HITOP 100W Adjustable Aquarium Heater Submersible

HITOP 100W Adjustable Aquarium Heater Submersible

$12-$184.3
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Example Calculations

13 Medium Hermit Crabs

Inputs

Crab Count3
Crab SizeMedium

Result

Tank20-gallon long
Substrate Depth6 inches
Extra Shells12

Gallons = (5 + 2×5) × 1.5 = 22.5, rounds to 20-gallon long. Substrate = 6" for medium crabs. Shells = 3 × 4 = 12.

22 Large Hermit Crabs

Inputs

Crab Count2
Crab SizeLarge

Result

Tank20-gallon long
Substrate Depth8 inches
Extra Shells8

Gallons = (5 + 1×5) × 2 = 20. 20-gallon long fits. Substrate = 8" for large crabs. Shells = 2 × 4 = 8.

Frequently Asked Questions

Q

How big of a tank do hermit crabs need?

Plan 5 gallons for the first hermit crab and 5 gallons per additional crab. A 10-gallon tank is the minimum for 2 crabs, but larger tanks maintain humidity much better.

  • 1–2 small crabs: 10-gallon minimum (20 × 10 × 12 inches)
  • 3–4 medium crabs: 20–29 gallon (30 × 12 × 18 inches)
  • 5+ crabs or jumbo size: 40–55 gallon or larger
  • Larger tanks are easier to maintain proper humidity (70–80%)
  • Glass tanks hold humidity better than wire or mesh enclosures
CrabsTank SizeSubstrate (qt)Extra Shells
2 small10-gallon78
3 medium20-gallon long2312
4 large40-gallon breeder5416
3 jumbo55-gallon9012
Q

How deep should hermit crab substrate be?

Substrate must be deep enough for the largest crab to fully bury itself for molting. Minimum is 6 inches for medium crabs, up to 12 inches for jumbo crabs.

  • Small crabs (dime-sized shells): 4 inches minimum depth
  • Medium crabs (quarter-sized): 6 inches minimum depth
  • Large crabs (golf ball): 8 inches minimum depth
  • Jumbo crabs (baseball+): 10–12 inches minimum depth
  • Mix 5 parts play sand with 1 part coconut fiber at sandcastle consistency
Q

How many extra shells do hermit crabs need?

Provide 3–5 extra shells per crab in graduated sizes. Crabs need options to switch into as they grow, and having choices reduces shell fights.

  • Offer 3–5 shells per crab in slightly larger sizes than current shell
  • Natural turbo and tapestry shells are most popular with hermit crabs
  • Avoid painted shells — paint chips are toxic and chipping exposes sharp edges
  • Include some shells slightly larger AND same size for comfort switching
  • Boil new shells in dechlorinated saltwater before adding to the tank
Q

What temperature and humidity do hermit crabs need?

Hermit crabs need 75–85°F temperature and 70–80% humidity. Both salt and fresh dechlorinated water pools are required for gill health.

  • Temperature: 75–85°F (below 70°F causes lethargy and death)
  • Humidity: 70–80% (below 65% causes gill damage and suffocation)
  • Use under-tank heater (UTH) on the back wall, NOT under the substrate
  • Both freshwater and saltwater pools deep enough for crabs to submerge
  • Use marine salt mix (not table salt) for the saltwater pool

Related Calculators

Terrarium Calculator

Calculate terrarium setup

Aquarium Calculator

Calculate tank volume

Ant Farm Calculator

Calculate formicarium size

Axolotl Tank Calculator

Calculate axolotl tank volume, chiller size, and filter requirements. Get setup recommendations by axolotl count and room temperature for healthy care.

Betta Fish Tank Calculator

Calculate betta fish tank setup: heater wattage, filter size, water change schedule, and plant count. Get recommendations by tank size and room temperature.

Hedgehog Cage Size Calculator

Calculate hedgehog cage size, exercise wheel diameter, and heating pad wattage. Get habitat recommendations by cage type, hedgehog count, and temperature.

Related Resources

Garden Watering Calculator: How Much Water Does Your Garden Really Need?

Read our guide

How Much Paint Do I Need for a Room? Complete Calculator Guide

Read our guide

How Many Tiles Do I Need? Tile Calculator Guide for Floors & Walls

Read our guide

Terrarium Calculator

Calculate terrarium setup

Reptile Enclosure Calculator

Calculate reptile tank size

Ant Farm Calculator

Calculate formicarium size

More Pet Calculators

Calculate needs for all your animals

View All

Last Updated: Mar 19, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

UseCalcPro
FinanceHealthMath

© 2026 UseCalcPro