About TankMath

TankMath is a set of free calculators for people who keep fish, shrimp, plants and corals.

What we do

Fishkeeping involves a surprising amount of math: how many gallons a tank really holds, how much gravel to buy, how big a heater to get, how much water to change to bring nitrate down, how many grams of fertilizer to dose. Getting these numbers wrong can cost money, or worse, livestock.

Each TankMath calculator is built around a clearly stated formula. Next to every tool you will find how it works, a worked example you can check by hand, the assumptions behind the result, and the sources the numbers come from.

How we build each calculator

1. Research. We start from published references: measurement standards, chemistry data, engineering formulas and established fishkeeping guidance.
2. Cross-check. Where sources disagree, we say so on the page and explain which default we chose and why.
3. Test. The calculator's output is checked against the worked example on its page and against edge cases.
4. Update. Each page shows when it was last reviewed. If you spot a mistake, please tell us.

Important note

Our calculators give estimates for hobby use. They are not a substitute for the instructions on your equipment, the label on a medication or fertilizer, or advice from a qualified aquatic veterinarian. For large or tall DIY tanks, have the design checked by a professional.

Privacy

All calculations run in your browser. The numbers you type are not sent to us. See our privacy policy for details about cookies and advertising.