Aquarium Calculator
Enter the inside length, width and height of a fish tank to find its volume in US gallons and liters and roughly how much the water weighs.
Aquarium volume formula
US gallons = length × width × height (inches) ÷ 231
There are 231 cubic inches in a US gallon. For liters, measure in centimeters and divide by 1,000.
Worked example
A tank 48 × 13 × 21 in holds 13,104 ÷ 231 = 56.7 gallons (214.7 liters). The water alone weighs about 473 lb, so a stand must be strong enough.
Why volume matters
- Water treatment and medication doses are given per gallon.
- Heater and filter sizes are rated by tank volume.
- Stocking guidelines depend on how much water there is.
Frequently asked questions
How much does a 55-gallon aquarium weigh?
The water alone is about 460 lb, and with glass, substrate and decor a full tank can exceed 600 lb.
Should I use inside or outside dimensions?
Inside dimensions, measured to the water level, give the most accurate volume.
How do I convert gallons to liters?
Multiply by 3.785.
Does gravel reduce the volume?
Yes. Substrate, rocks and ornaments displace water, often 10–20% of the total.
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