Aquarium water volume calculator

Measure the water, not the label.

A tank sold as 20 gallons does not necessarily hold that amount at its working waterline. Outside dimensions include glass and trim. Use the inside length and width, and measure to the actual water surface.

Substrate, rocks and equipment displace water. Connected sumps contain their own working volume. This calculator leaves those values to you instead of applying an invisible default deduction.

For a cylinder, measure the internal diameter and water height. Bowfront and corner tanks can use measured fill: total marked container amounts with all contents installed. Do not use their rectangular bounding box as water capacity. Account for water retained in porous material and connected equipment without counting it twice.

Itemize filled-system weight once working water is known.

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Aquarium substrate quantity worksheet

For a rectangular bed with an even front-to-back slope, use inside length × width × average depth. This estimates bulk substrate volume, including spaces between grains. It is not water displacement or weight.

Divide by the bag’s labeled volume and round up for whole bags. If sold by mass, use that exact substrate’s documented coverage or density; sand, gravel and soil do not share one pounds-per-liter conversion. This worksheet does not select a depth for plants or livestock. Follow the chosen material’s preparation instructions.