What Is the Turtle Tank Size Calculator?
This calculator estimates the minimum aquarium size your pet turtle needs based on its shell length. It uses the popular aquarist rule of thumb of 10 gallons of water per inch of shell length. A properly sized tank gives your turtle room to swim, dive, and stay healthy, while making it far easier to keep the water clean.
How to Use It
Measure the straight-line length of your turtle's carapace (top shell) in inches — measure across the shell, not over its curve. Enter that number, then choose how many turtles will share the tank. The result shows the minimum recommended volume in US gallons and the equivalent in liters. Always round up to the next available tank size; bigger is always better for water quality.
The Formula Explained
The core calculation is simple:
$$\text{Min Gallons} = \text{Shell Length (in)} \times 10$$
For more than one turtle, the calculator keeps the full requirement for the largest turtle and adds 50% of the base volume for each additional turtle, since turtles need both swimming space and territory.
Worked Example
A red-eared slider with a 6-inch shell needs: $$6 \times 10 = 60 \text{ gallons}$$ minimum. If you keep two turtles of that size, the second adds 30 gallons (50% of 60), for a total of 90 gallons.
FAQ
Is 10 gallons per inch enough? It's a sensible minimum for water volume. Aquatic turtles produce a lot of waste, so going larger improves water quality and reduces maintenance.
Does the tank need to be full of water? Aquatic turtles also need a dry basking area. The gallon figure refers to swimming water volume, so pick a tank that holds at least this much when filled to a safe level.
What about baby turtles? Hatchlings grow quickly. Buy a tank sized for the turtle's expected adult shell length to avoid frequent upgrades.
