**Flow metering instrumentation for measuring the volume of a substance that has passed a particular point in a specified time period.**

A volumetric flow meter is an instrument which can measure either directly or indirectly the volume of a substance which is passing through a specific location in a set period of time.

Many volumetric flow meters actually measure the speed of the flow rather than directly measure the volumetric flow rate. The flow speed measurement is converted into a volumetric flow rate by multiplying the flow velocity by the cross-sectional area of the duct or pipe where the volumetric flow meter is installed, i.e. Q = v · A.

Volumetric flow meters can provide an instantaneous analogue, digital or pulse output of the volumetric flow rate.

A volumetric flow meter may also include additional electronics such as a digital indicator for displaying the total volume measured to date.

The measurement of volumetric flow is called the volumetric flow rate, and this is defined as the amount of volume that will be transferred in a unit period of time i.e. Q or V̇ = V / t.

Volumetric flow can be measured either directly using a volumetric flow meter, or indirectly by measuring the flow speed or a pressure drop created by a shaped obstacle. The volumetric flow rate can then be derived using mathematical formulas and other fixed parameters such as cross-sectional area, density etc…

There are many different units used for measuring volumetric flow rate. The type of substance, size of cross sectional area, flow speed, and geographic region, will all dictate the volume and time units which are the most convenient to use for a particular flow measurement. Popular volumetric flow rate units litres or gallons per second, minute or hour (L/s, L/m, L/h, gps, gpm, gph).