To provide a gravity intravenous set with high accuracy flow volumetric measurement.

A method and a device for volumetric measurement of a drop of fluid administered in a gravity intravenous set 12 are provided. Radiation 28, preferably infrared light is passed through from the exterior of the drip chamber 14 of the intravenous set and is detected and quantified by a receiver 32 on the other exterior side of the chamber. The radiation passing through the chamber when a drop is not passing through the radiation path is taken as the background radiation level. When a droplet falls in the chamber, loss occurs in radiation which passes through droplet in the chamber and reaches the receiver. The volume of the droplet is calculated corresponding to a relative loss of the radiation value with respect to the background radiation value.