Basic rectangular-tank volume
Multiply length, width, and water height in centimeters, then divide by 1,000 for liters. A 60 × 30 × 36 cm water space is theoretically about 64.8 L.
Use internal dimensions and the real water line when possible. Water height is not the full external height of the tank.
- Volume (L) = length × width × water height ÷ 1,000
- Prefer internal measurements and the real water line
- Curved and cylindrical tanks need different geometry
Why substrate and decor matter
Sand, soil, rock, wood, and internal equipment displace water. Exact displacement is hard to measure for porous and irregular materials.
Treat a displacement percentage as an estimate and refine it with the volume of water actually used during later water changes.
Water-change calculation and example
Multiply real volume by the planned change rate. A 30% change in a 50 L aquarium requires about 15 L of prepared replacement water.
Topping up evaporation replaces water loss but does not remove the same waste as a water change. Keep top-up and change volumes separate.
- Replacement water = real volume × change rate
- 50 L × 30% = 15 L
- Separate evaporation top-up from water changes
What matters after the volume
Correct liters do not protect livestock from a large temperature, chlorine, pH, or hardness difference. Dose conditioners using the product label and the relevant water amount.
Nitrate does not fall by the exact change percentage when replacement water also contains nitrate. Consider both source-water readings and the rise between changes.