🐠 Aquarium Volume Calculator
Enter your tank's shape and dimensions to see how much water it really holds — gallons, litres, and a net volume that accounts for substrate and décor, so you can stock and dose with confidence.
🧮 Calculate Your Tank Volume
What is an Aquarium Volume Calculator?
It turns a few tape-measure readings into the number that underpins nearly every fishkeeping decision: how much water your aquarium actually holds. Punch in the length, width, and height (or the diameter and height for a round tank) in inches or centimetres, and it returns US gallons, litres, and the raw cubic volume in an instant.
Because substrate, rocks, and décor displace water — and you never fill right to the rim — it also gives a net volume trimmed by about 10%. Use the net figure whenever you stock fish, dose conditioner, or add medication, so treatments land at the right strength and your tank isn't quietly overstocked.
❓ Frequently Asked Questions
How do I calculate my aquarium's volume in gallons?
For a rectangular tank, multiply length × width × height in inches to get cubic inches, then divide by 231 to get US gallons. For a round (cylinder) tank, use π × radius² × height. This calculator does both for you and also converts to litres — just pick your shape and units and enter the measurements of the water area, not the outside of the glass.
Why is the 'net' volume lower than the calculated volume?
A tank never actually holds its full geometric volume. Substrate, rocks, driftwood, and décor displace water, and you leave a gap of an inch or two below the rim you never fill. The net figure trims about 10% off to reflect the real water volume, which is the number you should use when stocking fish or dosing treatments and conditioners.
Should I dose medication and conditioner on gross or net volume?
Dose on the true (net) water volume, not the box size printed on the tank. A heavily aquascaped tank can hold noticeably less water than its nominal rating, so dosing on the gross number risks overdosing. When in doubt, err toward the net figure and follow the product label.
How do I measure a tank I don't know the dimensions of?
Measure the inside length, width, and the height of the water column (not the full glass height) with a tape measure. For a cylinder or bowfront, measure the diameter across the widest point. Enter those numbers here in either inches or centimetres and the calculator handles the conversion.