Fish Tank Stocking Calculator
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Suggested Fish Counts by Tank Size
Approximate counts for small community fish with standard filtration
| Tank Size | Neon Tetras (1") | Guppies (2") | Corydoras (2") | Platys (2.5") |
|---|---|---|---|---|
| 10 gallon | 8-10 | 4-5 | 4-5 | 3-4 |
| 20 gallon | 15-18 | 8-10 | 8-10 | 6-8 |
| 29 gallon | 20-25 | 12-14 | 12-14 | 10-11 |
| 40 gallon | 30-35 | 18-20 | 15-18 | 14-16 |
| 55 gallon | 40-50 | 25-27 | 20-25 | 18-22 |
| 75 gallon | 55-70 | 35-37 | 30-35 | 25-30 |
How We Calculate This
This fish tank stocking calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
The calculator uses the classic inch-per-gallon rule as a starting point, then adjusts for fish bioload (waste production) and filtration capacity.
The basic rule:
- Base rule: 1 inch of fish per gallon of water
- Filter adjustment: basic (0.8×), standard (1.0×), heavy (1.2×) multiplies effective capacity
- Bioload factor accounts for messy fish (goldfish, oscars) needing more water per inch
- Stocking percentage: green (0-75%), yellow (75-100%), red (over 100%)
- This rule works best for small, slim-bodied community fish under 3 inches
The inch-per-gallon rule is a rough guideline. Large-bodied, messy fish like goldfish and oscars need much more space. Always research specific species requirements and monitor water parameters with a test kit.
When Would You Use This Calculator?
This fish tank stocking calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
Is the 1 inch per gallon rule accurate?
It is a reasonable starting point for small community fish (tetras, guppies, rasboras). It breaks down for large-bodied fish, messy fish, and territorial species. A 10-inch oscar does not belong in a 10-gallon tank.
How do I know if my tank is overstocked?
Test water weekly. Rising ammonia or nitrite, or nitrate above 40 ppm before water changes, suggests overstocking. Other signs: fish gasping at the surface, aggression, or needing water changes more than once a week.
Do plants help with stocking levels?
Yes. Live plants absorb ammonia and nitrate, effectively increasing your tank's capacity by 10-20%. A heavily planted tank can handle a slightly higher bioload than a bare tank with the same filtration.
What is bioload?
Bioload is the amount of waste a fish produces. A 6-inch goldfish produces far more waste than six 1-inch neon tetras, despite the same total inches. Messy eaters, large-bodied fish, and bottom feeders tend to have higher bioload.