Aquarium volume calculator

Enter your tank's inside measurements to see how many gallons it holds, how much it weighs when full, and what size heater and filter it needs.

Length

Width (front to back)

Height

Units

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US gallons (full tank)

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Liters

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Real water after gravel and decor

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Approx. filled weight

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Heater size

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Filter flow

These are estimates using common rules of thumb. Measure the inside of the glass for the most accurate result.

Gear for a 20 gallon tank

Heater: look for about 100 watts.
Filter: rated for at least 100 gallons per hour.
Stand: must hold about 200 lb. Never put a full tank on regular furniture.
Test kit: a liquid test kit for ammonia, nitrite and nitrate (every tank needs one).

How to calculate aquarium volume

For a rectangular tank, multiply length × width × height in inches, then divide by 231 to get US gallons. A standard 24 × 12 × 16 inch tank is 4,608 cubic inches, or just under 20 gallons.

For a round (cylinder) tank, the formula is 3.1416 × radius × radius × height. The radius is half the diameter.

In centimeters, multiply length × width × height and divide by 1,000 to get liters.

Why your tank holds less water than its size

Gravel, rocks, decorations and the gap left at the top all take up space. Most tanks hold about 85 to 90 percent of their listed volume in real water. Use the real water figure when dosing medicine or water conditioner.

How much does a fish tank weigh?

Water weighs about 8.3 pounds per gallon. Once you add glass, gravel and decor, a good rule is about 10 pounds per gallon. A 55 gallon tank weighs roughly 550 to 600 pounds when set up, which is why a proper stand matters.

What size heater and filter do I need?

Most tropical fish do well with 3 to 5 watts of heater per gallon. Use the higher end if your room is cold. For filters, aim for one that moves 4 to 6 times the tank's volume every hour, so a 20 gallon tank needs a filter rated for 80 to 120 gallons per hour.