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Aquarium Volume Calculator

Calculate aquarium water volume in liters, US gallons, imperial gallons, cubic inches, and cubic feet for common tank shapes.

Calculate Aquarium Volume

Aquarium Volume Estimate

Estimated Water Volume 0 L
US Gallons 0 gal
Imperial Gallons 0 gal
Cubic Meters 0 m3
Cubic Feet 0 ft3
Cubic Inches 0 in3
Approx. Water Weight 0 kg
The result represents the calculated water volume from the dimensions and selected fill level. Actual water capacity will be lower when substrate, rocks, decorations, filters, and other equipment occupy space inside the aquarium.

What Is an Aquarium Volume Calculator?

An aquarium volume calculator estimates how much water a fish tank holds from its dimensions and shape. The result helps with aquarium setup, water changes, filtration planning, medication dosing, stocking calculations, and maintenance.

This calculator supports rectangular, cube, cylindrical, and hexagonal aquarium shapes. Enter the tank dimensions, choose the measurement unit, and select the expected water fill level.

How to Calculate Aquarium Volume

A rectangular aquarium uses length, width, and height to determine the internal volume.

Volume = Length × Width × Height

The calculator converts the result into liters and other common volume units. A fill percentage then adjusts the theoretical capacity to estimate the amount of water inside the tank.

Rectangular Aquarium Formula

For a rectangular tank, multiply the three internal dimensions together.

Liters = Length × Width × Height ÷ 1,000

This formula applies when all three dimensions are measured in centimeters.

Cylindrical Aquarium Formula

A cylindrical aquarium uses the radius and height of the tank.

Volume = Pi × Radius × Radius × Height

The calculator uses the entered diameter to determine the radius automatically.

Hexagonal Aquarium Volume

A regular hexagonal tank uses the side length and height of the hexagonal prism.

Volume = (3 × square root of 3 ÷ 2) × Side × Side × Height

Enter the hexagonal side length in the Length field when the hexagonal shape is selected.

Why Actual Water Volume Is Lower

A tank's advertised capacity often represents its theoretical internal volume. The actual amount of water inside a working aquarium is usually lower.

  • Gravel and aquarium substrate occupy space.
  • Rocks and driftwood displace water.
  • Decorations take up internal volume.
  • Filters and other equipment occupy space.
  • Aquariums are often filled below the top edge.
For medication dosing: Use the estimated amount of water actually present in the aquarium rather than the manufacturer's advertised tank size. Follow the medication label and product instructions for dosing.

How Much Does Aquarium Water Weigh?

Fresh water weighs roughly 1 kilogram per liter under ordinary conditions. The calculator uses this relationship to provide an approximate water weight.

The total weight of a filled aquarium is higher because the tank itself, substrate, rocks, decorations, equipment, and stand also add weight.

Aquarium Volume Conversion

  • 1 US gallon = approximately 3.785 liters
  • 1 imperial gallon = approximately 4.546 liters
  • 1 cubic meter = 1,000 liters
  • 1 cubic foot = approximately 28.317 liters
  • 1 cubic inch = approximately 0.01639 liters

Frequently Asked Questions

For a rectangular aquarium, multiply the internal length by width by height. The result is then converted into liters, gallons, or other volume units.

One US gallon equals approximately 3.785 liters. One imperial gallon equals approximately 4.546 liters.

No. The calculated volume represents the geometric tank volume adjusted for the selected fill level. Gravel, rocks, driftwood, decorations, and equipment displace water and reduce the actual water volume.

A 20 US gallon aquarium has a nominal capacity of about 75.7 liters. The actual water volume is lower once substrate, decorations, equipment, and the desired fill level are considered.

Fresh water weighs roughly 1 kilogram per liter. A 100-liter volume therefore weighs about 100 kilograms before adding the weight of the aquarium, stand, substrate, rocks, and equipment.

Actual water volume helps with water-change planning, filtration sizing, maintenance, and aquarium treatment calculations. Tank dimensions alone often overstate the amount of water present during normal use.