Fish Tank Stocking Calculator

How it is calculated

All three dimensions go in as centimetres: length, width and height, where the height should be the water depth rather than the glass height. Volume is litres = L × W × H / 1000, since 1,000 cubic centimetres make one litre. US gallons are litres × 0.264172, shown with one decimal. The stocking figure follows the old inch-per-gallon rule converted to metric, total adult fish length = litres × 0.67 cm, rounded to a whole number. It is a total length for all fish combined, counted at adult size. The tool takes the full rectangular volume: it subtracts nothing for gravel, rocks or decorations, and it ignores filtration, species and temperature.

Common mistakes

• Entering the outside dimensions in inches or metres. The fields are centimetres; 1 m should be typed as 100.
• Using the glass height instead of the water level. A tank filled to 5 cm below the rim holds noticeably less, and the volume and stocking number are overstated.
• Counting the length of young fish bought at the shop. The total should use adult size, which is what the fish will grow to.
• Forgetting that gravel, rockwork and wood displace water. The tool gives the gross volume, so the real water is lower.
• Treating the total centimetres as permission to mix any species. Heavy-bodied fish such as goldfish or large cichlids need far more space than their length suggests.