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Short answer
A flowmeter measures how much fluid moves past a point, and the main types differ in what they sense: tube vibration (Coriolis), pressure drop across a restriction (differential pressure), electromagnetic induction (magnetic), vortices shed by the fluid (vortex) or sound waves (ultrasonic). The fluid decides which type fits: conductive liquids suit magnetic meters, steam and clean gas suit vortex meters, and high-accuracy mass flow suits Coriolis meters.
This guide is general device information for lab, clinic and facilities staff. It is not medical advice and gives no flow-rate settings.
Definition and scope
A flowmeter (also written flow meter) is an instrument that quantifies the flow of a liquid or gas. Two readings are common. Volumetric flow reports the volume that passes per unit of time. Mass flow reports the mass that passes per unit of time. Which one a given meter reports follows from its measuring principle, which is why the type matters when specifying or replacing one.
The term covers industrial process meters and the gas-flow devices fitted to medical oxygen supplies. This page explains the process-measurement principles; for the medical oxygen case, see oxygen regulators and the flowmeter types used with medical oxygen. A peak flow meter, which measures how fast a person can exhale, is a different device, covered in what a peak flow meter is.
How flowmeters measure flow in practice
Each type infers flow from a physical effect rather than counting fluid directly. Emerson, a flow-measurement manufacturer, describes the principles this way (page checked 2026-10-30):
- Coriolis meters measure mass flow directly using tube vibration.
- Differential pressure meters calculate flow from the pressure drop across a primary element.
- Magnetic meters measure volumetric flow based on fluid conductivity and electromagnetic induction.
- Vortex meters detect vortices shed by the flowing fluid to determine velocity.
- Ultrasonic meters use sound waves to measure flow velocity, either inline or non-intrusive.
Flowmeter types compared by fluid and use
The table restates the manufacturer’s own description of each type and the applications it names. It is a starting point for a conversation with the supplier, not a selection rule.
| Type | What it senses | Applications the manufacturer names |
|---|---|---|
| Coriolis | Mass flow, directly, using tube vibration | High-accuracy mass flow and custody transfer |
| Differential pressure | Pressure drop across a primary element | Steam, gas and legacy installations |
| Magnetic | Volumetric flow via electromagnetic induction in a conductive fluid | Conductive liquids such as water and slurry |
| Vortex | Vortices shed by the flowing fluid, giving velocity | Steam and clean gas |
| Ultrasonic | Flow velocity from sound waves, inline or non-intrusive | Non-intrusive or high-precision measurement of liquids and gases; clamp-on style where interrupting the process is not feasible |
Match the meter to the fluid
- Conductive liquid such as water: the manufacturer says magnetic meters are suited to conductive liquid applications.
- Steam or clean gas: vortex meters are described as well suited; differential pressure meters are described as widely used.
- You need mass flow directly, at high accuracy: Coriolis.
- You cannot interrupt the process or penetrate the pipe: non-intrusive ultrasonic, which the manufacturer lists for temporary measurements, energy audits and retrofit installations.
Where it matters for labs, clinics and supply decisions
A flowmeter reading is only as trustworthy as its calibration chain. The US National Institute of Standards and Technology (NIST) maintains primary standards for gas flows from 0.01 standard cm3/min to 103 standard m3/min, and offers calibration services for gas flow, liquid flow, airspeed and liquid volume (NIST Fluid Metrology, checked 2026-10-30). NIST also calibrates working-standard flow meters and supports flowmeter manufacturers and calibration laboratories.
For a facility that relies on a flowmeter, this makes calibration status a question to ask about any meter, whatever its type. Related CASRAI guides cover what calibration is, how to read a calibration certificate and how calibration intervals are set.
Common misunderstandings
A flowmeter is not a regulator
A flowmeter shows or measures flow. A regulator is a separate device. For medical oxygen, the oxygen regulator guide sets out the flowmeter variants (Thorpe tube and Bourdon gauge) and how they relate to a regulator.
Volumetric flow and mass flow are different readings
Magnetic meters are described as measuring volumetric flow; Coriolis meters measure mass flow directly. Comparing readings from the two types without knowing which quantity each reports can mislead.
Accuracy and precision are not the same
A meter can repeat the same reading consistently and still be off from the true value. See accuracy versus precision in measurement.
FAQ
What are the main types of flowmeter?
Coriolis, differential pressure, magnetic, vortex and ultrasonic are the five principles described by Emerson. Multiphase and watercut metering are listed by the same manufacturer as products, without a stated principle.
Which flowmeter type suits water?
The manufacturer states that magnetic meters suit conductive liquid applications such as water and slurry.
Can a flowmeter be fitted without cutting into the pipe?
Non-intrusive ultrasonic models are described as suited to cases where interrupting the process is not feasible.
Who calibrates flowmeters?
NIST offers gas-flow and liquid-flow calibration services and calibrates its own working-standard flow meters; it also supports flowmeter manufacturers and calibration laboratories.
Sources
- Emerson, Flow measurement, emerson.com/en-us/automation/measurement-instrumentation/flow-measurement, checked 2026-10-30.
- NIST, Fluid Metrology, nist.gov/pml/sensor-science/fluid-metrology, checked 2026-10-30.
