ToolnozaAquarium volume: the short answer
For a rectangular tank measured internally in centimeters, liters = length × width × water depth / 1,000. A 60 × 30 cm footprint filled to 35 cm contains 63 liters before substrate and decorations displace water.
Use actual water depth for the water volume and full internal height for theoretical tank capacity. The two results differ when the aquarium is not filled to the top.
Measure the inside of the tank
Measure internal length and width, then the water depth you intend to use. Exterior measurements include the glass and can overestimate capacity. Choose either centimeters or inches for every dimension.
If you start from millimeters, divide by ten to get centimeters. If you start from meters, multiply by one hundred. Do not mix a length in centimeters with a width in inches.
Worked example: capacity versus actual water
Consider a tank with internal dimensions 60 × 30 × 40 cm. Full capacity is 60 × 30 × 40 / 1,000 = 72 L. Filling it to 35 cm gives 63 L before displacement.
With your estimated displacement allowance of 10%, usable water = 63 × (1 − 0.10) = 56.7 L. Converted to US gallons, 56.7 / 3.785411784 ≈ 14.98 US gal. The 10% is an example input, not a universal allowance.
Liters, US gallons and inches
One US liquid gallon equals 3.785411784 liters. The calculator uses US gallons, not Imperial gallons. Divide liters by this factor to get US gallons.
For inch inputs, each dimension is converted with 1 inch = 2.54 cm before the rectangular volume formula is applied. Because volume multiplies three dimensions, the combined conversion factor is 2.54³.
Substrate displacement and model limits
Substrate and objects reduce available water volume. Enter an allowance based on your own setup; the calculator cannot measure it. If the tank is filled using known container volumes, the amount actually added can help check the estimate.
This model is for rectangular tanks. Bow-front, cylindrical and irregular tanks need different geometry. It does not determine fish stocking, filtration capacity, water chemistry or treatment doses. Do not assume full nominal capacity equals the water currently present.