Aquarium Volume Calculator
A 36 x 18 x 16 inch tank holds about 44.9 US gallons, and that water alone weighs roughly 374 pounds. This aquarium volume calculator turns your tank's length, width, and height into gallons and liters, plus the water weight your stand and floor have to carry. That last number surprises most first-time fishkeepers.
Quick answer
Volume is length x width x height, converted from cubic inches or centimeters to gallons and liters.
Volume
44.9 US gallons (169.9 L)
Liters
169.9
Water weight
374.6 lb (169.9 kg)
What this tells you
- •Volume is length x width x height, converted from cubic inches or centimeters to gallons and liters.
- •One US gallon is 231 cubic inches, and one liter is 1,000 cubic centimeters.
- •Water weighs about 8.34 lb per gallon (1 kg per liter), before glass, gravel, and rock.
- •Real water volume runs 10 to 15 percent below the tank calculation once substrate, decor, and the fill line are counted.
How to Use
- 1Measure the tank's length, width, and height, inside dimensions if you want to be precise.
- 2Pick inches or centimeters.
- 3Read the volume in US gallons and liters.
- 4Check the water weight before choosing a stand or placement, and add roughly 20 percent for glass and substrate.
How It Works
Formula
gallons = L x W x H (inches) / 231Multiply the three dimensions to get cubic inches, then divide by 231, the cubic inches in a US gallon. A 36 x 18 x 16 tank is 10,368 cubic inches, and 10,368 / 231 = 44.9 gallons. In metric, cubic centimeters divided by 1,000 gives liters directly, which is why metric tank math is so much cleaner.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Standard 40-gallon breeder
Nominal 40-gallon tanks calculate a bit above their name. Water weight: about 374 lb.
Common 60 x 30 x 30 cm tank
The classic European starter tank, holding 54 liters brim full.
10-gallon starter tank
2,400 cubic inches over 231, with water weighing about 87 lb.
Standard Aquarium Sizes
Common tank names against their calculated volume and water weight.
| Tank | Dimensions (in) | Volume | Water weight |
|---|---|---|---|
| 10 gallon | 20 x 10 x 12 | 10.4 gal | 87 lb |
| 20 gallon long | 30 x 12 x 12 | 18.7 gal | 156 lb |
| 40 breeder | 36 x 18 x 16 | 44.9 gal | 374 lb |
| 55 gallon | 48 x 13 x 21 | 56.7 gal | 473 lb |
| 75 gallon | 48 x 18 x 21 | 78.5 gal | 655 lb |
| 125 gallon | 72 x 18 x 21 | 117.8 gal | 982 lb |
Common mistakes
- Measuring outside the glass. Panels are 6 to 12 mm thick, and outside dimensions overstate a large tank by a gallon or more.
- Forgetting the tank never fills to the brim. Substrate, hardscape, and the waterline typically remove 10 to 15 percent.
- Ignoring water weight. A filled 75-gallon setup approaches 850 lb with glass and rock, beyond many pieces of furniture.
- Stocking fish by nominal tank name instead of actual volume. A heavily scaped 40 breeder may hold 35 real gallons.