Aquarium Volume & Substrate Calculator
This tool was built by Serge (MSc) using established science and government sources. My academic background covers plant biology, environmental biology, and biogeochemistry. My tools are for educational purposes and give practical guidance, not professional advice.
Knowing your tank's real volume matters for stocking, dosing, and water changes, and the number printed on the box is often rounded. This calculator works out the volume of a rectangular aquarium from its measurements, and estimates how much substrate you need for a planted tank at your chosen depth. It gives volume in litres, US gallons, and UK gallons.
Tank volume:
This is the full geometric volume. Real water volume is a little less once substrate, rocks, and equipment take up space.
How this works
Tank volume is length times width times water height. I convert your measurements to one unit, work out the volume, and then convert it to litres, US gallons, and UK gallons. For substrate, I use the tank's floor area, length times width, times the substrate depth you enter, which gives the volume of gravel or aquasoil to buy.
Understanding your result
The volume is what the tank holds filled to the water height you gave. Your real water volume will be a little lower, since substrate, hardscape, and equipment take up room, so for dosing and stocking many aquarists work to about 90 percent of this figure. For a planted tank, a substrate depth of around 5 to 8 centimetres gives roots room while sloping higher at the back looks good and aids planting.
Important limitations
This is for rectangular tanks. Bow-front, cylindrical, and other shapes hold different amounts and are not covered here. The volume is geometric, so it does not subtract glass thickness, substrate, or decor, all of which lower the true water volume. Treat it as a close upper figure.
Scientific basis
The calculation uses standard geometric volume and unit conversions. For water measurement and volume references I draw on public science resources:
Related reading
My guide on aquarium substrate covers choosing the right base for a planted tank, and my article on aquascaping tools helps you plant and shape it. My guide on CO2 systems for planted aquariums pairs with a healthy substrate.
This calculator is for educational purposes and general guidance only. It is not professional aquarist advice. Confirm stocking and dosing against your specific setup and livestock needs.