Aquarium Volume Calculator – Find Your Fish Tank Capacity
Determining fish tank volume has never been easier. With this aquarium calculator, you can find the water volume of your tank in a blink of an eye. Choose between 7 typical aquarium shapes — from a simple rectangular box, through cylindrical variations, to bow front tanks — and get results instantly in US gallons, UK gallons, liters, cubic centimeters, cubic inches, and cubic feet.
Both metric (cm) and US imperial (inches) measurement systems are supported.
Aquarium Shapes
This calculator supports seven popular fish tank shapes:
| Shape | Description |
|---|---|
| Rectangular Prism | Standard box-shaped aquarium — the most common type |
| Cube | Equal-sided aquarium — all edges the same length |
| Bow Front | Curved front glass for a wider viewing angle |
| Corner Bow Front | Designed to fit in a room corner with a bow-shaped glass |
| Cylinder | Full cylindrical tank, often used as a decorative centerpiece |
| Half Cylinder | Flat-backed cylinder, ideal for wall mounting |
| Quarter Cylinder | Corner-fitting cylindrical tank taking up a quarter circle |
Formulas Behind the Fish Tank Calculator
Rectangular Prism
The standard aquarium volume formula:
V = height × width × length
Cube
A cube-shaped aquarium — raise the edge length to the power of 3:
V = edge³
Cylinder and Its Fractions
For a full cylindrical aquarium:
V = π × (diameter / 2)² × height
For a half-cylinder (flat back):
V = π × (diameter / 2)² × height / 2
For a quarter cylinder (corner tank):
V = π × (diameter / 2)² × height / 4
Bow Front Aquarium
The bow front volume combines a rectangular prism with a circular segment:
V = height × width × length + circular segment volume
Where the circular segment uses:
- Sagitta (bow depth) = full_width − width
- Chord = length (front width)
- Arc radius r = (chord² / 4 + sagitta²) / (2 × sagitta)
- Central angle θ = 2 × arcsin(chord / (2r))
- Segment volume = 0.5 × r² × (θ − sin θ) × height
Corner Bow Front Aquarium
The corner bow front is half the bow segment:
V = bow segment volume / 2
How to Use This Aquarium Gallon Calculator
- Choose the measurement system — Metric (cm) or US Imperial (inches).
- Select your tank shape from the dropdown.
- Enter the dimensions — the required fields will appear automatically based on the shape you selected.
- Click "Calculate Volume" — results appear instantly in multiple units: US gallons, UK gallons, liters, cm³, in³, and ft³.
Example: How Big Is a 75-Gallon Aquarium?
Curious about a 75-gallon tank? A typical 75-gallon rectangular aquarium has the following dimensions:
- Length: ~48 inches (122 cm)
- Width: ~18 inches (46 cm)
- Height: ~21 inches (53 cm)
That gives a volume of 48 × 18 × 21 = 18,144 in³ ≈ 78.5 US gallons (≈ 297 liters) — intentionally oversized so you never overfill it. Tank sizes are nominal, not exact.
Volume Unit Conversion Reference
| Unit | Equivalent |
|---|---|
| 1 US Gallon | 3.785 liters |
| 1 UK (Imperial) Gallon | 4.546 liters |
| 1 Liter | 1,000 cm³ |
| 1 Cubic Inch | 16.387 cm³ |
| 1 Cubic Foot | 28.317 liters |
Important Note
The calculated volume is the geometric volume of the tank. The actual fillable water volume will be less because:
- Glass walls have a small but measurable thickness
- Substrate (gravel, sand) takes up space at the bottom
- Equipment such as filters, heaters, and decorations displace water
- You typically fill the tank only 90–95% of its capacity
Use this result as an estimate when planning your aquarium setup, choosing a filter, heater, and calculating the required amount of water conditioner.