Betta Tank Size Calculator
Measure your tank's length, width, and water depth, enter them below, and this tool tells you the exact volume in gallons and liters — plus an instant verdict on whether it's big enough for a betta.
Calculate your tank volume
Use inches or centimeters — pick a unit, then enter the three numbers.
Tip: measure the water depth (how high you actually fill the tank), not the tank's total height. Gravel, rocks and decorations take up space too, so your real usable volume is a bit less than the number above.
How to use it
- Measure the inside of your tank: length × width across the base.
- Measure the water depth from the bottom to your normal fill line (usually an inch or two below the top).
- Enter the three numbers, pick your unit, and hit Calculate.
What the verdict means for a betta
| Volume | Betta verdict | Why |
|---|---|---|
| Under 2.5 gallons | Too small | Bowls and small jars can't keep water stable — avoid |
| 2.5 – 5 gallons | Below recommended | Workable but unstable for a beginner; upgrade if you can |
| 5 gallons | Yes — recommended minimum | Best starting point for a single betta |
| 10+ gallons | Yes — ideal | More water = more stable, easier to maintain |
Long and low beats tall. Bettas like horizontal swimming room. A 5-gallon "long" or a 10-gallon rectangular tank gives them more usable space than a tall narrow one of the same volume.
Ready for the next step? Once you've picked a tank, you'll need to heat it properly and cycle it before adding fish. Not sure what size to buy? See what size tank a betta needs.