Aquarium Volume Calculator

Measure the inside of your tank in inches. You'll get the volume in US gallons, UK gallons and liters, plus how heavy it will be when full.

How the calculation works

• Rectangle: length × width × height
• Cylinder: π × (diameter ÷ 2)² × height
• Bow front: a rectangle plus the curved part. We approximate the bow as a half-ellipse: length × back width × height + (π ÷ 4) × length × bow depth × height, assuming the bow adds about a quarter of the width.

Divide cubic inches by 231 for US gallons, or by 277.4 for UK gallons. One US gallon is 3.785 liters, and a gallon of fresh water weighs about 8.34 lb.

Worked example

A standard "29 gallon" tank is 30 × 12 × 18 inches outside. Filled to 17 inches inside, it holds 30 × 12 × 17 = 6,120 cubic inches, or about 26.5 US gallons. Glass thickness, gravel and decor mean the real water volume is usually 10 to 15% less than the label.

Frequently asked questions

How much does a full aquarium weigh?

Plan for about 10 lb per gallon once you include glass, gravel and rock. A 55 gallon tank can weigh 600 lb or more, so put it on a stand rated for it, ideally against a load-bearing wall.

What size heater do I need?

A common rule is 3 to 5 watts per US gallon, using the higher end if the room is cold. Two smaller heaters are safer than one big one.

How many fish can I keep?

The old "one inch of fish per gallon" rule is only a rough start, and fails for big-bodied or messy fish. Check each species' adult size and minimum tank size, and filter for at least 4 times the tank volume per hour.