Built by Aquarium
Enthusiasts, for
Enthusiasts

TankMate is a free, open-access aquarium stocking calculator designed to help freshwater hobbyists plan healthy, compatible fish communities. We created this tool because we've been through the same experience — standing in a fish store, unsure if that school of tetras will fit alongside the corydoras we already planned for.

How the Calculator Works

Our tool goes beyond the basic "one inch per gallon" rule. We use bioload multipliers that account for the fact that a slim neon tetra produces significantly less waste than a heavy-bodied goldfish. We also factor in:

• • Water displacement — 10% reduction for gravel, hardscape, and equipment
• • Filtration quality — bonus capacity for good and excellent filter setups
• • Minimum school sizes — enforces social requirements for schooling species
• • Species compatibility — warns about potentially incompatible tankmates
• • Minimum tank sizes — prevents you from adding fish that need more space

Important Limitations

This calculator provides general guidance only and should not replace proper research. Many factors affect safe stocking levels that our tool cannot account for, including:

• • Planted vs. unplanted tanks (plants improve water quality)
• • Water change frequency and volume
• • Feeding amount and frequency
• • Individual fish temperament (some fish are more aggressive than their species norm)
• • Tank dimensions (a tall narrow tank has less surface area than a wide shallow one)

When in doubt, always stock less than the maximum. Your fish will thank you.

Our Fish Database

We currently cover 25 of the most popular freshwater aquarium species, including tetras, livebearers, rasboras, corydoras, gouramis, small cichlids, and a few specialty species. Each entry includes adult size, temperature range, pH preferences, bioload rating, minimum school size, and compatibility data based on widely accepted community tank guidelines.

We're continuously expanding our database. If there's a species you'd like to see added, please let us know.

Support This Project

TankMate is completely free to use. We cover hosting and development costs through display advertising. If you find this tool helpful, the best way to support us is to bookmark the page, share it with fellow hobbyists, and come back whenever you're planning a new tank.