Fish Tank Volume Calculator
Calculate aquarium volume in gallons or liters from tank dimensions. Plus stocking estimate.
What is a 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.