Fish Tank Volume Calculator in Feet

Working in feet

If you measured your tank in feet, the calculator converts to volume for you. Multiply length, width and height in feet to get cubic feet, then convert to litres and gallons.

How to calculate tank volume in feet

1. Measure the length, width and height in feet. Use decimals for part feet: 6 inches is 0.5 ft, 3 inches is 0.25 ft, 9 inches is 0.75 ft.
2. Multiply the three numbers to get cubic feet.
3. Convert: 1 cubic foot holds about 28.3 litres, 7.48 US gallons or 6.23 UK gallons.

Example: a 4 x 2 x 2 foot tank is 16 cubic feet. 16 x 28.3 = about 453 litres, or 16 x 7.48 = about 120 US gallons.

How many litres is a 3 foot fish tank?

“3 foot tank” only tells you the length. The width and height change the answer a lot:

• 3 x 1 x 1 ft (36 x 12 x 12 inches): 3 cubic feet, about 85 litres or 22.4 US gallons.
• 36 x 12 x 16 inches (3 ft long, 1 ft deep, 16 inches tall): about 113 litres or 29.9 US gallons.
• 36 x 18 x 16 inches, the “40 gallon breeder”: about 170 litres or 44.9 US gallons.
• 3 x 1.5 x 1.5 ft (36 x 18 x 18 inches): 6.75 cubic feet, about 191 litres or 50.5 US gallons.

So a 3 foot tank can hold anywhere from about 85 to 190 litres. Measure the width and height before you buy equipment for it.

These are outside sizes. The water in a set-up tank will be lower; see the water volume calculator.

Tanks measured in feet and inches

Measurements like “4 ft 2 in” are easy to get wrong. Either convert the inches to a decimal of a foot (2 / 12 = 0.17, so 4.17 ft), or switch the calculator to inches and enter 50 (4 x 12 + 2). Don’t enter 4.2: that is 4 feet 2.4 inches.

Other common lengths

• 2 ft tank (24 x 12 x 12 inches): about 56.6 litres or 15 US gallons.
• 4 ft tank (48 x 18 x 18 inches): about 254.9 litres or 67.3 US gallons.
• 5 ft tank (5 x 2 x 2 ft): about 566 litres or 149.6 US gallons.
• 6 ft tank (6 x 2 x 2 ft): about 680 litres or 179.5 US gallons.

The table above lists more sizes measured in feet.

Cubic feet and weight

A cubic foot of fresh water weighs about 62.4 lb (28.3 kg). A 6 cubic foot tank therefore carries about 374 lb of water before glass and gravel. For tanks of 3 feet and up, check the full weight with the fish tank weight calculator before choosing a stand.

For measurements in inches, use the calculator in inches. For the result in gallons only, use the gallon calculator.