Quick answer
Tank volume in litres = length × width × height (cm) ÷ 1,000, and US gallons = litres ÷ 3.785. A 100 × 40 × 50 cm tank holds 200 L, or 52.83 US gallons.
Enter length, width and water height in centimetres. The calculator returns litres and gallons. Use this aquarium tank volume calculator to check your own figures.
Related tools: Volume of a Hemisphere Calculator: Volume and surface area of a hemisphere. Rectangular Prism Volume Calculator: Volume of a rectangular prism (box). Triangular Prism Volume Calculator: Volume of a triangular prism.
How to use the Aquarium Tank Volume Calculator
- Enter length (cm) (above 0).
- Enter width (cm) (above 0).
- Enter water height (cm) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Length | A number, in cm | > 0 |
| Width | A number, in cm | > 0 |
| Water height | A number, in cm | > 0 |
Formula and method
Formula
litres = l × w × h ÷ 1000; US gallons = litres ÷ 3.785411784
IEEE-754 double precision; shown to at most 6 decimal places.
1 L = 1000 cm³ and 1 US gallon = 3.785411784 L exactly.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Length = 100; Width = 40; Water height = 50.
| Result | Value |
|---|---|
| Volume | 200 L |
| US gallons | 52.83441 |
Example 2
Inputs: Length = 60; Width = 30; Water height = 30.
| Result | Value |
|---|---|
| Volume | 54 L |
| US gallons | 14.265291 |
The first line is the headline result (volume). Below it the aquarium Tank Volume Calculator lists uS gallons, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Water weight
200 L of water weighs 200 kg, plus the glass, stand and gravel. Check the floor and stand rating before filling. Fill to the actual water line, not the rim.
Rectangular tanks only
For a bow-front, hexagon or cylinder tank, use the right shape formula. Decor and substrate displace water, so actual volume is 5 to 10% less.
How the result changes with length
Holding every other input at the first worked example, this table changes only length. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Length | Volume | US gallons |
|---|---|---|
| 50 | 100 L | 26.417205 |
| 100 | 200 L | 52.83441 |
| 200 | 400 L | 105.668821 |
| 400 | 800 L | 211.337642 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Length: entering "0" shows "Length must be greater than 0." beside that field and no result.
Choosing between the Aquarium Tank Volume Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Volume of a Hemisphere Calculator](/math/volume-of-hemisphere/) | radius | Volume |
| [Rectangular Prism Volume Calculator](/math/rectangular-prism-volume/) | length, width and height | Volume |
| [Triangular Prism Volume Calculator](/math/triangular-prism/) | triangle base, triangle height and prism length | Volume |
| [Cylinder Volume Calculator](/math/cylinder-volume-calculator/) | radius and height | Volume |
| [Sphere Volume Calculator](/math/sphere-volume-calculator/) | radius | Volume |
Background: geometry measurements
Geometry results carry units that depend on the quantity: a perimeter or length is in linear units such as cm, an area or surface area is in square units (cm²) and a volume is in cubic units (cm³). Use one length unit for every input, because the calculator multiplies the numbers as given.
Flat (2D) shapes have an area and a perimeter; solids (3D) have a surface area and a volume. Two familiar checks: a circle of radius r has area πr² and circumference 2πr, and a sphere has volume (4/3)πr³ and surface area 4πr².
Assumptions and limitations
- Rectangular tank only
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for length to confirm this.
Frequently asked questions
How many fish per litre?
Depends on species, not a simple rule.
What is a 20 gallon tank in litres?
A 20 US gallon tank holds 20 × 3.785 = 75.7 litres.
Should I use inside dimensions?
Yes. Inside dimensions and the actual water height give the real capacity; glass thickness is excluded.
What does the Aquarium Tank Volume Calculator calculate?
Volume of a rectangular tank in litres and US gallons. It returns Volume and US gallons.
What formula does the Aquarium Tank Volume Calculator use?
litres = l × w × h ÷ 1000; US gallons = litres ÷ 3.785411784. 1 L = 1000 cm³ and 1 US gallon = 3.785411784 L exactly.
What do I need to enter in the aquarium Tank Volume Calculator?
You enter Length (cm), Width (cm) and Water height (cm).
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Rectangular tank only.
What is an example of a aquarium Tank Volume result?
With length 100, width 40 and water height 50, the volume is 200 L.
Where does the method come from?
The method follows: NIST SP 811 (2008), Appendix B.8.
Related calculators
- Volume of a Hemisphere Calculator — Volume and surface area of a hemisphere.
- Rectangular Prism Volume Calculator — Volume of a rectangular prism (box).
- Triangular Prism Volume Calculator — Volume of a triangular prism.
- Cylinder Volume Calculator — Volume of a cylinder.
- Sphere Volume Calculator — Volume and surface area of a sphere.
- Cone Volume Calculator — Volume, slant height and surface area of a cone.
- Hypotenuse Calculator — Hypotenuse of a right triangle from its two legs.
- Rhombus Calculator — Area, side and perimeter of a rhombus from its diagonals.
- Ellipse Calculator — Area and approximate perimeter of an ellipse.
Sources
- NIST SP 811 (2008), Appendix B.8
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.