Fish Tank Volume Calculator
Calculate aquarium volume in gallons or liters from tank dimensions. Plus stocking estimate.
What is Fish Tank Volume Calculator?
The fish tank volume calculator converts dimensions to gallons. The "1 inch of fish per gallon" rule gives a rough stocking guide.
Formula
Volume (gallons) = L × W × H (in inches) ÷ 231. The 1-inch-per-gallon rule applies to small community fish.
Worked example
24×12×16 inch tank: 4,608 cu in / 231 = 19.9 gallons. Max ~20 inches of small community fish.
How to use this calculator
- Measure inside dimensions of the tank.
- Enter length, width, height.
- Volume in gallons and liters appears.
Frequently asked questions
Is the 1 inch per gallon rule accurate?
Rough rule of thumb. Better: research specific species. A 6-inch goldfish needs more than 6 gallons; small tetras can pack tighter. Bioload (waste production) varies.
Why measure inside dimensions?
Glass thickness reduces internal volume. Outside measurements overestimate by 5–10%. For accurate volume, measure inside.
Account for substrate and decor?
Subtract ~10% for gravel and decorations. A "20-gallon tank" actually holds ~18 gallons of water in practice.
Saltwater vs freshwater stocking?
Saltwater fish need more space (typically 1 inch per 3 gallons). Reef tanks even more. Bigger is always better for both ecosystems.