Aquarium Stocking, Heater & Filter Sizer
Estimate aquarium volume, stocking and equipment
Aquarium stocking, heater & filter FAQ
What does this aquarium calculator actually estimate?
This page turns your internal tank measurements into an estimated water volume in liters and US gallons. It then adds a conservative starter stocking suggestion for your chosen freshwater tank type, along with an equipment checklist for heater wattage and filter flow (LPH/GPH) that matches that volume.
Is this calculator only for freshwater tanks?
Yes. The math and presets are tuned for beginner-friendly freshwater setups like community tanks, planted tanks, betta tanks, goldfish, cichlids and shrimp. It does not account for marine sumps, reef rock displacement, complex plumbing or specialist filtration, so you shouldn’t use it as a primary sizing tool for saltwater systems.
How accurate are the stocking suggestions?
Stocking lines here are deliberately conservative starting points, not hard limits. They assume gradual stocking, decent filtration and regular maintenance. Real-world stocking needs vary a lot with species, adult size, behavior, aquascape and water change routine, so always adapt the advice to your exact fish and local conditions.
How do you calculate heater wattage?
Heater sizing is based on a simple watts-per-gallon rule of thumb that depends on the temperature rise between room and tank water. A small temperature lift uses fewer watts per gallon; larger lifts use more. The calculator multiplies your estimated gallons by that watts-per-gallon figure to give a total heater wattage that will usually be split across one or two heaters.
How do you choose the filter flow range?
Filter flow is expressed as a turnover range, i.e. how many times per hour the filter can move the full tank volume. Gentle setups like betta and shrimp use lower turnover, while goldfish and cichlids use higher turnover to cope with heavier waste. The tool maps your selected tank type to a typical turnover band and converts that to LPH and GPH targets you can compare against filter specs.
Which units does the tool support?
You can work in Imperial (inches and °F) or Metric (centimeters and °C). The units selector applies to both tank measurements and temperatures, and everything is converted behind the scenes so the volume, heater and filter estimates are consistent no matter which system you prefer.
Does this replace research and water testing?
No. This calculator is meant as a planning and sanity-check tool only. It can help you decide whether a tank size, heater and filter combination is broadly sensible, but it does not replace species-specific research, cycling the tank, testing water parameters or monitoring real fish behavior over time.
How to use this aquarium stocking, heater & filter sizer
This aquarium calculator turns rough tank measurements into a clear plan for volume, stocking and equipment. It estimates how much water your tank actually holds, suggests a conservative starting stock level, and gives you a heater wattage and filter flow range that match your freshwater setup.
1. Enter your tank size in inches or centimeters
Start by adding the internal length, width and water height of your tank. You can work in inches and °F (Imperial) or centimeters and °C (Metric) — the units selector keeps both dimensions and temperatures in sync. The calculator assumes the tank is filled to about 95% of its internal height to allow for rims, substrate and top clearance.
2. Choose a freshwater tank type and temperatures
Next, pick a freshwater tank type such as community, planted, betta-only, goldfish, cichlids or shrimp. This drives the stocking suggestion and the filter turnover range. Then add your typical room temperature and your desired water temperature. The tool uses the difference between these two values to estimate heater wattage.
3. Read the summary for a clear tank & gear plan
The results box highlights a headline such as “80 L (~21 gal) community tank” plus a short stocking note and an equipment checklist. You’ll see suggested heater watts, an estimate of the temperature rise, and a filter flow range in LPH and GPH. This makes it easy to check whether a tank size, heater and filter combination is sensible for the fish you want to keep.
4. Use it for planning, upgrades and quick “what if” checks
Use this aquarium sizer when planning a new tank, upgrading from a smaller setup or sanity-checking a second-hand aquarium. Try a few “what if” scenarios: change tank size, switch tank type or adjust target temperature to see how heater and filter recommendations move. The Copy summary button gives you a clean, text-only breakdown you can paste into notes, messages or a stocking spreadsheet.
Remember that this tool focuses on beginner-friendly freshwater guidance. It does not replace species-specific research, water testing or regular maintenance. Always adapt stocking and equipment choices to your fish, your aquascape and how often you can care for the tank.
How the aquarium sizing math works
This calculator models your aquarium as a rectangular box. Let L, W and H be the internal length, width and water height in centimeters. The tool assumes the tank is filled to about 95% of the entered height to reflect rims, substrate and the space you leave at the top.
The approximate water volume in liters is:
Liters ≈ L × W × H × 0.95 ÷ 1000
All inches you enter are converted to centimeters internally, and liters are converted to US gallons using:
Gallons ≈ Liters ÷ 3.785
Heater wattage uses a watts-per-gallon rule of thumb tied to the temperature rise between room and water. Let ΔT be that rise in °C. The calculator uses roughly:
– 3 W/gal for ΔT ≤ 3 °C
– 4 W/gal for ΔT between 4–6 °C
– 5 W/gal for larger temperature rises
The estimated heater wattage is then:
Heater watts ≈ tank gallons × W/gal(ΔT)
Filter flow is based on turnover, the number of times per hour the filter can move a full tank volume. Gentle setups like betta or shrimp tanks use lower turnover; goldfish and cichlids use higher turnover. If k is the turnover factor, then:
Flow (LPH) = liters × k
Flow (GPH) = gallons × k
Different tank types map to different turnover ranges (for example, 3–4× for betta, 5–7× for community, 7–10× for messy fish). The tool shows the resulting flow as a range in LPH and GPH so you can compare it to filter specs.
Stocking suggestions use simple, conservative rules: small community fish get roughly one fish per few liters, goldfish get much more water per fish, and shrimp start in small colonies. These are designed as starting points, not strict limits. Always adjust for adult size, body shape, behavior, aquascape, water change schedule and the performance of your particular filter.
References and further reading
Helpful guides on aquarium stocking, heater sizing and filter turnover:
- LiveAquaria — filter turnover explained – Overview of flow rates and matching filters to tank size.
- The Spruce Pets — heater wattage by tank size – Heater sizing charts and practical examples.
- Practical Fishkeeping — stocking density FAQ – Discussion of stocking approaches and common pitfalls.
- AquariumScience — in-depth heater analysis – Technical look at heater sizing and performance.
Use these resources as general guidance only. Always tailor your final stocking and equipment choices to your specific species, water parameters and maintenance routine.