Fish Tank Dimensions Calculator

From dimensions to volume

For a rectangular tank, volume equals length times width times height. Keep all three measurements in the same unit, and the calculator converts the result to litres, gallons and cubic centimetres.

Which measurements does each tank shape need?

The calculator asks for different dimensions depending on the shape you pick. This is what to measure for each:

Always measure the height the same way: from the bottom glass to the rim for full capacity, or to the water line for the water you actually have.

How to measure fish tank dimensions accurately

• Use a rigid steel tape. Soft tailor’s tapes sag across long tanks and add length.
• Measure along the top edge. The top is easiest to reach and is not hidden by gravel or a stand.
• Ignore the plastic frame. Many tanks have black trim at the top and bottom. Measure the glass, not the trim.
• Measure twice on curved tanks. For a bow front, measure the width at the very centre of the curve and again at the flat ends. For a cylinder, measure across the top at two different angles and use the average.
• Write the unit down. Most mistakes come from mixing inches and centimetres.

Converting dimensions between inches and centimetres

1 inch = 2.54 cm, and 1 foot = 12 inches = 30.48 cm. You can enter dimensions in either unit, but if you need to convert a listing by hand:

• 36 x 18 x 18 inches = 91.4 x 45.7 x 45.7 cm
• 48 x 13 x 21 inches = 121.9 x 33.0 x 53.3 cm
• 60 x 30 x 30 cm = 23.6 x 11.8 x 11.8 inches

For measurements in feet and inches, such as 4 ft 2 in, convert everything to inches first: 4 x 12 + 2 = 50 inches. Then use inches for all three sides.

Outside dimensions vs inside dimensions

Shops list the outside dimensions, because that is what you need to fit the tank on a stand. The calculator gives the most accurate volume from the inside dimensions. To get the inside from the outside, subtract the glass thickness twice from the length and the width, and once from the height. You can see the thickness at the top edge of the glass. For new builds, the glass thickness calculator shows what thickness a tank of your size needs.

Dimensions to volume, at a glance

For a box-shaped tank, volume = length x width x height. In centimetres, divide by 1,000 for litres. In inches, divide by 231 for US gallons. The table above lists common metric tank dimensions with their volume. For other shapes, see the fish tank volume formula page, and for the standard US tank sizes, see standard fish tank dimensions.