Real numbers for the fish tank.

Fin & Figures — for the fish aficionado — free calculators for stocking, dosing, cycling, and planted and reef tanks. No guessing, just the numbers you need.

Browse All Tools

Browse by category

11 calculators

Tank Setup & Sizing

Volume, weight & stand load

4 calculators

Livestock & Feeding

Stocking, feeding & quarantine

8 calculators

Water Chemistry & Cycling

Dosing, cycling & heaters

3 calculators

Planted Tank

CO2, fertilizer & hardscape

4 calculators

Reef & Marine

Salinity, dosing & skimmers

5 finders

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Tank Volume Calculator

Get exact gallons or liters from your tank's inside dimensions — the single biggest search across the whole site.

Aquarium Stocking Calculator

Check bioload and stocking capacity for your tank size and fish community before you buy.

All AquariumCalcs tools

How AquariumCalcs works

Fishkeeping is full of small calculations: how many gallons a tank holds, how heavy it is when full, how much to dose, how big a heater or filter to buy, what a water change does to a reading. AquariumCalcs does the arithmetic and explains the thinking, so you can see how each answer was reached and where it came from. Each tool shows its method, says where a figure is a rule of thumb and reminds you that the label on your own product has the last word.

Where to start

Planning a tank: check the Tank Volume, Tank Weight and Stand Floor Load calculators before you buy.
Starting out: take the First-Tank Type Finder and read about cycling before you add fish.
Stocking: use the Aquarium Stocking Calculator, and research the adult size of every species.
Routine care: use the Water Change Calculator and the Heater Size Calculator.

Read more about the site, how we calculate and our disclaimer and safety notes. Spotted a mistake? Tell us.