Who built this
This site is maintained by hobbyists who got tired of guessing. Between us we have kept planted tanks, reef systems and breeding setups, and in every case the first thing we needed and the last thing the label told us was the real water volume. The calculators here are the ones we wanted to exist.
Why accuracy matters
Nearly every decision in fishkeeping is scaled to volume: how much medication, how much fertiliser, what size heater, how many fish, how much salt. A 20 percent error in volume becomes a 20 percent error in all of them. Most of that error comes from three places, and this site attacks each one: using the wrong shape formula, measuring outside the glass, and ignoring the water that substrate, rock and the fill gap take away.
Methodology
- Every shape uses the exact geometric formula for its footprint, listed on the formulas page. No lookup tables, no approximations where an exact formula exists.
- Conversions use defined constants: 231 cubic inches per US gallon, 3.785411784 litres per gallon, 16.387064 cubic centimetres per cubic inch.
- Fill height scales volume by the height ratio for vertical-walled tanks and by spherical segment geometry for bowls.
- Substrate is treated as a porous bed with 38 percent voids, so only the solid fraction is subtracted.
- Weight uses 8.34 lb per gallon for fresh water and a specific gravity of 1.025 for reef water.
What the site covers
Found a problem?
If a result looks wrong or a shape is missing, tell us. Include the dimensions you entered and the number you expected.