Free Aquarium Calculators
Stop guessing. Size your tank, stock it safely, and keep your water healthy with precise, easy-to-use aquarium calculators.
Fish Tank Stocking Calculator
How many fish can your aquarium safely hold? Based on tank size, species and filtration.
Tank Volume Calculator
Find your aquarium's gallons and liters from its dimensions — plus filled weight for your stand.
Aquarium Heater Calculator
What size heater does your tank need? Enter room and target temperature for a recommendation.
Aquarium Filter Calculator
Get the right filter flow rate (GPH) for tropical, goldfish, cichlid, planted or reef tanks.
Substrate Calculator
How much gravel or sand do you need? Calculate by tank dimensions and desired depth.
Water Change Calculator
How much water should you change? Based on your current and target nitrate levels.
Why use aquarium calculators?
Most aquarium problems — sick fish, algae blooms, cloudy water — come from three beginner mistakes: overstocking, undersized equipment, and irregular water changes. Each of our calculators targets one of these mistakes with simple math backed by widely accepted aquarium guidelines.
Whether you're setting up your first 10-gallon betta tank or planning a 75-gallon community aquarium, running the numbers first saves you money, time, and stressed fish.
How to plan a new aquarium in 5 steps
- Measure your space and use the tank volume calculator to see what fits.
- Pick your fish, then check the stocking calculator so you don't overcrowd.
- Size your heater with the heater calculator — tropical fish need stable warmth.
- Choose a filter rated for your tank using the filter calculator.
- Maintain it with regular water changes — the water change calculator tells you how much.