Qubit Systems provides gas flow meters and monitors in various ranges.  Simple rotameters can be used to measure flows manually from 2ml/min to 42L/min. Mass flow monitors are used with data interface and software to measure gas flows up to 2LPM. Custom flow monitors for high flow rates are also available.

Flowmeters
A Flow Meter
Flow Monitor 1LPM
Flow Monitor 1L / Min
Flow Monitor 2LPM
Flow Monitor, Pump 1LPM
Flow Monitor, Pump 2LPM