Aquarium Volume Calculator
Gallons in a rectangular fish tank.
Enter your values
Enter the tank length in in.
Enter the tank width in in.
Enter the tank height in in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Total volume
- 50.5 gal
- Recommended fill volume (90%)
- 45.4 gal
- Weight when full (approx)
- 421 lb
Quick answer
Aquarium volume in gallons is length times width times height in inches, divided by 231.
gallons = (length x width x height in inches) / 231
At a glance
| What it does | Gallons in a rectangular fish tank. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Tank length, Tank width, Tank height |
| Main output | Total volume |
| Formula | gallons = (length x width x height in inches) / 231 |
| Cost | Free — no sign-up, no download |
How to use the Aquarium Volume Calculator
- 1Measure the tank's interior length, width and height in inches.
- 2The calculator uses the standard conversion of 231 cubic inches per US gallon.
- 3Use the 90% fill estimate to leave room at the top and avoid overflow with decor and substrate.
Inputs explained
- Tank length(in)
- Enter the tank length in in.
- Tank width(in)
- Enter the tank width in in.
- Tank height(in)
- Enter the tank height in in.
Worked example
Using the values the calculator loads with:
Inputs
- Tank length36 in
- Tank width18 in
- Tank height18 in
Results
- Total volume50.5 gal
- Recommended fill volume (90%)45.4 gal
- Weight when full (approx)421 lb
Frequently asked questions
Why not fill the tank 100%?
Leaving headspace prevents overflow when adding substrate, decorations or during water changes.
How much does a full tank weigh?
Water weighs about 8.34 lb per gallon, plus the tank, stand, substrate and decor weight on top of that.
What do I need to enter into the Aquarium Volume Calculator?
Just 3 values: tank length, tank width, tank height. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Aquarium Volume Calculator work out the answer?
Aquarium volume in gallons is length times width times height in inches, divided by 231. It applies the formula gallons = (length x width x height in inches) / 231 and shows the working so you can check each step by hand.
Is the Aquarium Volume Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.