Aquarium volume calculator

What is an aquarium volume calculator?

An aquarium volume calculator works out how much water a fish tank holds based on its dimensions. Knowing the volume is essential for stocking fish responsibly, dosing water treatments and fertilizers correctly, and choosing a filter and heater of the right size. This calculator supports five common tank shapes: rectangular, cube, cylindrical (round), bow-front, and hexagonal tanks.

How does the calculator work?

First pick the tank shape, then enter the dimensions it asks for:

• Rectangular — length, width, and height.
• Cube — a single side length.
• Cylinder — diameter and height.
• Bow front — length, width (the flat depth at the sides), height, and the bow depth (how far the curved front bulges out past the sides).
• Hexagonal — the edge length of one side and the height.

The calculator applies the shape’s formula, returns the water volume in your chosen unit (liters, gallons, cubic centimeters, and more), and also shows the approximate weight of the water.

The internal dimensions are what matter, so measure the inside of the glass and subtract anything that displaces water (substrate, rocks, decorations) if you want the true water volume rather than the full tank capacity.

Formulas

For a rectangular tank with length $l$, width $w$, and height $h$:

$$V = l \cdot w \cdot h$$

For a cube with side $s$:

$$V = s^3$$

For a cylindrical tank, the radius is half the diameter $d$, so $r = d/2$, and with height $h$:

$$V = \pi r^2 h = \pi \left(\frac{d}{2}\right)^2 h$$

For a bow-front tank, the volume is the rectangular body plus the curved bulge at the front. Modeling the bulge as a half-ellipse of depth $b$ (the bow depth) over the length $l$, with flat depth $w$ and height $h$:

$$V = l \cdot w \cdot h + \frac{\pi \cdot l \cdot b \cdot h}{4}$$

For a regular hexagonal tank with edge length $s$ and height $h$:

$$V = \frac{3\sqrt{3}}{2} \, s^2 \, h$$

Water weight follows directly from volume: one liter of fresh water weighs about one kilogram, so $1 \text{ L} \approx 1 \text{ kg}$.

Worked examples

Example 1: rectangular tank

A rectangular aquarium measures 100 cm long, 40 cm wide, and 50 cm high:

$$V = 100 \cdot 40 \cdot 50 = 200000 \, \text{cm}^3 = 200 \, \text{L}$$

That tank holds about 200 liters of water, weighing roughly 200 kg.

Example 2: cube tank

A cube aquarium with a 40 cm side:

$$V = 40^3 = 64000 \, \text{cm}^3 = 64 \, \text{L}$$

This nano-style cube holds about 64 liters, weighing roughly 64 kg.

Example 3: cylindrical tank

A cylindrical aquarium has a diameter of 40 cm and a height of 50 cm, so the radius is 20 cm:

$$V = \pi \cdot 20^2 \cdot 50 \approx 62831.85 \, \text{cm}^3 \approx 62.83 \, \text{L}$$

This round tank holds about 62.83 liters, weighing roughly 62.83 kg.

Example 4: bow-front tank

A bow-front aquarium is 100 cm long, 40 cm deep at the sides, 50 cm high, with a 20 cm bow:

$$V = 100 \cdot 40 \cdot 50 + \frac{\pi \cdot 100 \cdot 20 \cdot 50}{4} \approx 278539.82 \, \text{cm}^3 \approx 278.54 \, \text{L}$$

This bow-front tank holds about 278.54 liters, weighing roughly 278.54 kg.

Example 5: hexagonal tank

A hexagonal aquarium has an edge length of 40 cm and a height of 50 cm:

$$V = \frac{3\sqrt{3}}{2} \cdot 40^2 \cdot 50 \approx 207846.10 \, \text{cm}^3 \approx 207.85 \, \text{L}$$

This hex tank holds about 207.85 liters, weighing roughly 207.85 kg.

Practical notes

• The bow-front volume is an approximation: the curve of the front glass varies by manufacturer, so treat the result as a close estimate rather than an exact figure.
• Account for displacement: gravel, large rocks, and ornaments reduce the actual water volume, often by 5–15%.
• Saltwater is denser than fresh water (about 1.025 kg/L), so a marine tank weighs slightly more than the freshwater estimate.
• Always consider the total weight, including the tank, stand, substrate, and equipment, when checking that your floor and stand can support it.