A calculator for the water volume (capacity) of an aquarium or tank from its dimensions. Choose the shape — rectangular (width × depth × height) or cylinder (diameter × height) — and enter the inner sizes in centimeters (cm). It gives the full capacity in liters (L), cubic meters (m³), weight of water (approx. kg, water is about 1 kg/L) and US gallons (gal). A rectangular tank uses width × depth × height, and a cylinder uses π × (diameter ÷ 2)² × height for the volume in cm³, divided by 1000 to get liters. Enter a water level and it computes the effective volume of a partly filled tank (a cistern or storage tank) up to that level; set the level to 0 to use the height above as a full tank. Handy for working out how much water an aquarium (e.g. a 60cm tank) needs, dosing amounts for treatments, or checking the capacity of a storage tank. Every calculation runs in your browser; the sizes you enter are never sent to any server or API.