A rotameter is a flow meter device that measures the volumetric flow rate of a gas or fluid. It consists of a tapered tube with a moving internal float. Sometimes known as mechanical flow meters, gravity flowmeters or variable area flowmeters.

A rotameter is a gauge for measuring fluid flow using a graduated glass tube with an enclosed free float. Also known as variable area flow meters, rotameters are used to measure liquid or gas volumetric flow rates as they pass through the tapered tube of the rotameter.