About this tool
The fish tank stocking calculator estimates the maximum safe fish count for your aquarium based on water volume, fish size class, plant density, and filtration. It applies the modern volume-based approach rather than the outdated inch-per-gallon rule.
How it works
Max Fish = Effective Vol / Gal per Fish
Each fish type has a baseline gallon requirement. Live plants reduce bioload through nitrate uptake, adding 1 to 2 percent capacity each up to 25 percent. Filtration multiplier reflects waste removal efficiency. Stay below 80 percent of max for safety margin.
How to use the Fish Tank Stocking Calculator
The Fish Tank Stocking Calculator is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:
- Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
- Speed: results update as you type. No network round trip.
- Offline use: once the page is cached, it works without internet.
- No signup: no account, no email, no rate limits.
Step by step
- Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
- Read the result as it updates. The number reflects the formula commonly accepted in Fish Tank Stocking-related calculations.
- Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
- Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.
When you would use this
- Quick estimates: when you need a number now and don't want to open a spreadsheet.
- Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
- Comparison: running the same calculation with different inputs to compare options side by side.
- Learning: building intuition for how the underlying math behaves.
- Documentation: capturing a snapshot of inputs and outputs at a point in time.
Frequently asked questions
How many fish can I keep per gallon?
The classic rule is one inch of fish per gallon of water but this only works for small slim fish. Larger or messy fish need 3 to 5 gallons each due to higher waste output.
What is bioload?
Bioload is the total waste output of all fish in the tank. High bioload requires stronger filtration, more frequent water changes, and lower stocking density.
Do plants reduce bioload?
Yes, live plants absorb nitrogen waste and oxygenate the water, allowing 10 to 25 percent higher stocking density when the tank is well planted.
Can I overstock my aquarium?
Overstocking causes ammonia spikes, low oxygen, aggression, and disease. Stay within recommended limits and monitor water parameters weekly.
Is the Fish Tank Stocking Calculator accurate?
The Fish Tank Stocking Calculator applies the standard formula for fish tank stocking. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.
Is the Fish Tank Stocking Calculator free?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.
Are my inputs saved?
No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.
Can I use the Fish Tank Stocking Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum guidance.
How do I report a bug or suggest improvement to the Fish Tank Stocking Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours and update calculators when rules or formulas change.
How accurate is the Fish Tank Stocking Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Fish Tank Stocking Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Does the Fish Tank Stocking Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
Can I share results from the Fish Tank Stocking Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another fish tank stocking tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.