Input
How it works
Calculator sums per-turtle capacity using max(minimum gallons, gallons-per-inch × shell length). When planning for adults, it uses typical adult size per species or your override.
- Multiple turtles add 25% extra volume for territorial space.
- Filter turnover target: 5–8× tank gallons per hour.
- Heater sizing: ~3–5W per gallon depending on room temperature.
- Minimum footprint: length ≥ 5× largest shell; width ≥ 2× largest shell.
- Water depth: at least 2× largest shell with easy access to basking platform.
Species quick reference (typical adults)
| Species | Adult size (in) |
|---|---|
| Red-Eared Slider | 10 |
| Painted Turtle | 7 |
| Map Turtle | 9 |
| Common Musk | 5 |
| River Cooter | 12 |
| Common Snapping Turtle | 16 |
| Other / Unknown | 8 |
Lighting and environment tips
- Provide UVB lighting (5–10% output) sized to basking area; replace bulbs per manufacturer schedule.
- Maintain a stable basking spot around 88–95°F for most aquatic species; water 74–80°F depending on species and age.
- Secure lids and create gentle ramps; avoid sharp edges and entrapment hazards.
- Use dechlorinated water and test ammonia, nitrite, and nitrate regularly.
Why Tank Size Matters
Proper tank volume is more than a comfort upgrade—it directly affects filtration stability, swimming behavior, thermal gradients, and long‑term health. Undersized systems accumulate waste rapidly, forcing frequent water changes and stressing filtration. Oversized systems increase equipment cost but provide a safety buffer as juveniles grow. The goal of a Turtle Tank Size Calculator is therefore not a single “magic number,” but a structured estimate that combines turtle size, species behavior, stocking density, and husbandry practices.
The Core Sizing Formula
A widely used starting point for aquatic species (e.g., sliders, cooters, maps) is the 10 gallons per inch of straight carapace length (SCL) rule for the first turtle. For each additional turtle of similar size, add 5–10 gallons per inch depending on your filtration capacity and water‑change routine.
| Factor | Suggested Value | Notes |
|---|---|---|
| Base volume for first turtle | 10 × SCL (in) gallons |
Applies to active aquatic species; raise for strong swimmers. |
| Each additional turtle | 5–10 × SCL (in) gallons |
Use 10× if filtration is modest or feeding is heavy. |
| Basking & land area | Dedicated dry platform | Do not reduce water volume to “make room”—use an above‑tank basking dock. |
| Water depth | 1.5–2× carapace width (min) | Deeper is better for adults; juveniles need easy ramps and rests. |
| Filtration turnover | 4–6× tank volume per hour | External canister filters are preferred for turtles. |
Species Modifiers
Not all turtles use space the same way. Strong swimmers (sliders, painted turtles) reward deeper water and larger footprints. Bottom‑resters (musk, mud) prefer more structure and moderate depth. The table below offers conservative adult estimates for a single turtle; increase if your specimen is particularly active, if you keep multiple turtles, or if you feed heavily.
| Species (adult SCL) | Starter Minimum (gal) | Comfortable Range (gal) | Notes |
|---|---|---|---|
| Red‑Eared Slider (8–10") | 75 | 90–125 | Active swimmer; benefits from long tanks and deep water. |
| Painted Turtle (6–8") | 55 | 75–90 | Enjoys swim space; high UVB basking compliance. |
| Map Turtle (6–10") | 75 | 90–125 | Strong current tolerated; pristine water preferred. |
| Musk/Mud Turtle (3–5") | 30 | 40–55 | Shallower setups with abundant hides and rests. |
| Diamondback Terrapin (5–9") | 75 | 90–125 | Brackish‑tolerant; robust filtration and hardscape needed. |
Step‑by‑Step Sizing Method
- Measure SCL. Use calipers or a rigid ruler to capture straight carapace length to the nearest 0.25".
- Apply the base formula.
Volume = 10 × SCLfor the first turtle. - Adjust for species. Compare to the species table; choose the higher number.
- Account for growth. Juveniles often double or triple size; pick a tank that covers adult needs now to avoid frequent upgrades.
- Consider footprint. Long, wide tanks (e.g., 48–72" length) are superior to tall, narrow tanks.
- Plan for filtration. Select a canister filter rated at least 2× your calculated volume; target 4–6× hourly turnover.
- Design the basking area. Above‑tank docks preserve water volume and enable deeper swimming.
Worked Examples
Example 1 — Juvenile Slider (3.5" SCL): Base estimate is 10 × 3.5 = 35 gal. Because sliders are active and grow quickly, choose a 55–75 gal tank now; you will leverage the capacity as the turtle matures.
Example 2 — Adult Musk Turtle (4.25" SCL): Base estimate is 10 × 4.25 ≈ 43 gal. The species table suggests 40–55 gal, with emphasis on hides and moderate depth—select a 55‑gallon long for stable water and layout flexibility.
| Nominal Size | Typical Dimensions (L × W × H) | Notes for Turtles |
|---|---|---|
| 40 Breeder | 36" × 18" × 16" | Great footprint for musk/mud; easy basking dock placement. |
| 55 Gallon | 48" × 13" × 21" | Popular upgrade size; narrow width limits hardscape. |
| 75 Gallon | 48" × 18" × 21" | Balanced depth and width; ideal for many adult sliders. |
| 90–125 Gallon | 48–72" length, 18–24" width | Premium comfort for large/active species and multi‑turtle setups. |
Stocking, Bioload, and Maintenance
Turtles are messy feeders. Even with a large tank, uneaten food and high‑protein diets raise ammonia and nitrate. The practical consequence is that two tanks of equal volume can behave very differently depending on feeding style and filtration. A realistic plan includes: (1) a canister filter 2× the tank’s nominal rating, (2) pre‑filters to catch solids, (3) weekly partial water changes of 20–30%, and (4) regular testing for ammonia, nitrite, and nitrate. If your schedule allows only intermittent maintenance, select the larger end of the recommended volume range.
When the Calculator Suggests “Too Small”
If your calculation yields a volume below commercially available sizes, prioritize footprint and filtration, then compensate with conservative feeding, strong mechanical filtration, and more frequent water changes. Conversely, if the number is very large, ensure your stand, floor, and budget can support the final filled weight (roughly 8.3 lb per gallon / 1 kg per liter including glass and décor).
Quick Reference & Conversion
| Measure | Conversion | Use Case |
|---|---|---|
| US gal → liters | × 3.785 | Equipment rated in liters per hour. |
| Liters → US gal | ÷ 3.785 | Comparing international tank sizes. |
| Pounds of water | US gal × 8.34 | Stand/floor load planning. |
Key Takeaways
- Start with 10 gal per inch SCL for the first turtle; add 5–10 gal per inch for each additional turtle.
- Favor long, wide tanks and above‑tank basking to preserve water volume.
- Size filtration for 4–6× turnover and maintain consistent water‑change routines.
- Use species tables and your turtle’s behavior to refine the number upward as needed.
Disclaimer: These are conservative guidelines intended for planning. Always pair sizing with appropriate UVB lighting, basking heat, diet, and water quality monitoring. When in doubt, larger volumes and stronger filtration provide a safer margin.