Aquarium calculator
Aquarium volume calculator
Get true water volume in gallons and liters, with substrate subtracted, so your dosing and turnover targets are accurate.
True water volume
Enter your tank dimensions to see volume.
How it works
We multiply length × width × usable height (water height minus substrate), then convert cubic inches to gallons by dividing by 231, or cubic centimeters to liters by dividing by 1,000. The result is true water volume, not the nominal box size.
Common questions
- Why is true volume less than the listed tank size?
- Aquarium sizes are nominal. Glass thickness, rim, rock, and substrate all displace water, so true volume is typically 10 to 20 percent lower than the box number.
- Should I subtract substrate?
- Yes. Enter your substrate depth and the calculator removes that slice from the total. This makes turnover and dosing math accurate.
- What turnover rate should I target?
- Most freshwater tanks target 4 to 6 times the true volume per hour in filter flow. Reef tanks often run 10 times or more.