Turtle Tank Size Calculator
Minimum turtle tank gallons and depth from shell.
What it does
Turtles need room scaled to shell, not tank labels. Ten gallons per inch of straight carapace sets the floor, so a 6-inch turtle needs 60 gallons with 9 to 12 inches of water. Small tanks stunt growth and foul water within days.
The tool above runs the per-inch rule. Enter shell length and it prints minimum gallons, liters, and the depth band. Defaults show the 6-inch case at 60 gallons; a 4-inch turtle needs 40 with 6 to 8 inches of water.
Veterinary and welfare sources converge. PetMD care sheets state 10 gallons per inch with 1.5 to 2 times depth and publish the 4-inch to 40-gallon case, while RSPCA metric rules give 80 liters per 5 cm, landing within 8 % of the US figure. Both demand basking docks with UVB.
Depth and gear matter as much as volume. Water 1.5 to 2 times shell length lets turtles right themselves, filters turning 5x hourly hold ammonia down, and larger footprints beat tall narrow tanks. Measure yearly; upgrade before growth stalls.
How to use
- Measure straight shell length in inches.
- Read minimum gallons first.
- Read liters beside it.
- Set water depth in the printed band.
- Add dock, UVB, and 5x filter.
- Upgrade as the shell grows.
Formula
- shell
- Straight carapace length in inches.
PetMD states 10 gal per inch with 1.5-2x depth; RSPCA metric rule (80 L per 5 cm) cross-checks within 8 %.
Worked example
Example: 6 in turtle
Defaults: 6 in shell.
- Input: 6 in straight shell length.
- Gallons: 10 x 6 = 60.
- Liters: 60 x 3.78541 = 227.1.
- Depth: 1.5 x 6 to 2 x 6 = 9 to 12 in.
- Tool shows 60 gal minimum, 227.1 L, 9 to 12 in water.
Reference table
| Shell | Gallons | Depth |
|---|---|---|
| 3 in | 30 | 4.5-6 in |
| 4 in | 40 | 6-8 in |
| 5 in | 50 | 7.5-10 in |
| 6 in | 60 | 9-12 in |
| 8 in | 80 | 12-16 in |
| 10 in | 100 | 15-20 in |
Limits
- Minimums only; bigger always better.
- Rule per turtle; groups add 25 % each.
- Ignores species basking differences.
- Water chemistry needs test kits.
Common mistakes
- Small starter tanks for growers.
- Shallow water under 1.5x shell.
- Skipping UVB with the dock.
- Weak filters under 5x turnover.
- Never upgrading with growth.
Try it yourself
Quick checks. Answers sit tucked under each question.
4 in turtle?
10 x 4 = 40 gal. Liters 151.4. Depth 6 to 8 in.
8 in turtle?
10 x 8 = 80 gal. Liters 302.8. Depth 12 to 16 in.
Questions
How many gallons per turtle?
Ten gallons per inch of shell. A 6 in turtle needs 60 gal minimum.
How many liters?
Gallons times 3.78541. Here 227.1 L.
How deep should water be?
One and a half to two times shell length: 9 to 12 in here.
Does the metric rule agree?
Yes. RSPCA metric rule (16 L/cm) lands within 8 % of the US rule.
What about tankmates?
Add 25 % per extra turtle and apply the per-turtle rule to each.
What else does the tank need?
Yes. Basking dock, UVB light, and 5x filtration come with every size.