Turtle Tank Size Calculator: Gallons, Water Depth, Basking Area and Filter
How big a tank does your aquatic turtle need? Gallons from shell length and number of turtles, plus water depth, basking dock, filter and temperatures.
How it works
Minimum tank (US gal) = 10 × shell length (in) × (1 + 0.5 × (turtles − 1)) · Roomier target = 15 gal per inch · Water depth = 1.5–2 × shell length (musk and mud turtles 1–1.5×) · Basking dock per turtle ≈ 2 × 1.5 shell lengths · Filter rated for 2–3 × tank volume · 1 US gal = 3.785 L
The rule most keepers and turtle groups use is at least 10 US gallons of tank per inch of straight shell length (about 15 liters per centimeter). A 6 in red-eared slider therefore needs at least 60 gallons, and a 12 in adult female needs about 120. A more generous target of 15 gallons per inch gives extra swimming room and more stable water. Each extra turtle adds about half the first turtle’s volume, because turtles crowd and bite when space is tight. Water depth matters too. Sliders, cooters, painted and map turtles are strong swimmers and should have water at least 1.5 to 2 times their shell length deep, so they can dive and flip over. Musk and mud turtles walk on the bottom, so 1 to 1.5 times their shell length lets them reach the surface easily. Every turtle also needs a dry basking dock under a heat lamp and a UVB lamp; this calculator sizes it at about twice the shell length by one and a half times, per turtle. Turtles are messy eaters, so filters are usually rated for two to three times the tank volume. The temperatures shown follow red-eared slider care guidance (water 75–78 °F, 78–80 °F for hatchlings; basking spot 90–95 °F). These are rules of thumb, not species-specific veterinary advice. Unlike the tortoise enclosure calculator, which sizes dry land for tortoises, this calculator is for aquatic turtles that live in water.
Worked example
One 6 in red-eared slider: 6 × 10 = 60 US gal (227 L) minimum and 6 × 15 = 90 US gal roomier. Water should be 1.5 × 6 = 9 in to 2 × 6 = 12 in deep. The basking dock should be about 12 × 9 in, and the filter rated for 120–180 gal. The smallest common tank that holds 60 gal is a 75 gal (48 × 18 × 21 in). If the turtle is a female that will reach 12 in, plan for 120 gal.
Sources: RedEarSlider.com: Habitat (10 gallons per inch of shell, water temperatures) · RedEarSlider.com: Lighting and basking (basking spot 90–95 °F) · AllTurtles: Turtle tank size calculator (10 and 15 gal per inch, +50% per extra turtle) · Omni Calculator: Turtle tank size (10 gal per inch, musk turtle example) · Simple Decision Maker: Turtle tank sizing (water depth 1.5–2× shell, filter 2–3× volume)
Frequently asked questions
How many gallons does a turtle need?
At least 10 US gallons per inch of shell length, measured straight from front to back. A 4 in turtle needs 40 gallons, an 8 in turtle 80 gallons and a 10 in adult 100 gallons. 15 gallons per inch is a roomier target.
How big a tank do two turtles need?
Work out the tank for the largest turtle, then add about half again for each extra one. Two 8 in turtles need 80 + 40 = 120 gallons. Give each its own basking spot.
How deep should the water be in a turtle tank?
For swimmers such as sliders, cooters, painted and map turtles, make it at least 1.5 to 2 times the shell length: 9 to 12 in for a 6 in turtle. Musk and mud turtles prefer 1 to 1.5 times their shell length so they can reach the surface while walking on the bottom.
What size tank does a baby turtle need?
A 2 in hatchling needs at least 20 gallons, but a red-eared slider can reach 7 to 12 in within a few years. Many keepers start with the adult-size tank, or at least 40–50 gallons, to avoid buying several tanks as it grows.
What filter does a turtle tank need?
Turtles produce much more waste than fish, so choose a filter rated for two to three times your tank volume. For a 75 gal tank that means a filter rated for 150 to 225 gal, often an external canister.
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This calculator is for educational purposes. Double-check important results before acting on them.