How to choose the right flow meter for gas or liquid?
By Jan Willem Voortman, Webshopmanager · Last updated: 2 November 2026
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Quick answer: For gases (air, N₂, Ar, CO₂, He, H₂) choose a thermal mass flow meter: MASS-VIEW, MASS-STREAM or FLEXI-FLOW. For conductive water-based liquids (>20 µS/cm) choose a magnetic flow meter (MAG-VIEW). For non-conductive liquids such as deionized water choose a vortex flow meter (LIQUI-VIEW). Then narrow down by flow range, accuracy, pressure, temperature and output signal.
Key takeaways
- The medium decides the technology: thermal for gases, magnetic for conductive liquids, vortex for conductive and non-conductive liquids.
- Accuracy: from ± ~1% (FLEXI-FLOW) to ± 2% (MASS-VIEW).
- Pressure: all meters in this guide work up to 10–16 bar(g).
- Low flow: magnetic flow meters measure conductive liquids from 0.008 l/min.
- Budget: prices range from €195 (vortex) to €1,330 (thermal, MASS-STREAM).
In this guide
How to choose a flow meter in 6 steps
The right flow meter depends on more than the flow rate alone. Answer these six questions in order to find the right measurement principle and product for your application.
- Is your medium a gas or a liquid? Gases need a thermal mass flow meter. Liquids need a magnetic or vortex flow meter.
- Is your liquid conductive? Magnetic flow meters need a conductivity above 20 µS/cm (tap water, coolants, water-glycol). For deionized water or other non-conductive liquids, choose vortex.
- What is your minimum and maximum flow? Choose a meter whose range covers both, with your normal flow roughly in the middle of the range for the best accuracy.
- How accurate must the measurement be? For ± ~1%, choose FLEXI-FLOW. For process monitoring, ± 1.5–2% is usually sufficient.
- What are the pressure and temperature? Check the maximum pressure (10–16 bar(g)) and medium temperature in the table below.
- Which output, display and budget do you need? Analog or frequency for a PLC, RS-232/Modbus/FLOW-BUS for digital integration, Bluetooth for setup via a smartphone, or a local display for a quick readout.
Flow meter comparison table: which type fits your application?
Compare our flow measurement technologies by medium, specifications and price. On mobile, scroll the table horizontally.
| Criterion |  Magnetic flow meter(MAG-VIEW) | (LIQUI-VIEW) |  Digital VA alternative(MASS-VIEW) |  Thermal mass flow meter(MASS-STREAM) |  Smart thermal flow meter(FLEXI-FLOW) | |
|---|---|---|---|---|---|---|
| Media | ||||||
 | Gases (air, Ar, CO2, He, H2, N2, etc.) | ❌ No | ❌ No | ✅ Yes | ✅ Yes | ✅ Yes |
 | Conductive water-based liquids (>20 µS/cm) | ✅ Yes | ✅ Yes | ❌ No | ❌ No | ❌ No |
| Deionized water / non-conductive liquids | ❌ No | ✅ Yes | ❌ No | ❌ No | ❌ No |
| Specifications | ||||||
| Flow range | 0.008–250 l/min | 0.05-150 l/min | 10-2000 mln/min 0.04-500 ln/min | up to 1000 ln/min | 0-5 mln/min 1-500 ln/min | |
 | Output | Analog / frequency | Analog (4–20 mA) / frequency | RS-232 / Modbus / 0–5 Vdc | RS-232 / 4–20 mA | Modbus-RTU / FLOW-BUS Bluetooth |
 | Accuracy | ± 1.5% | ± 1–2% | ± 2% | ± 1.5% | ± ~1% |
 | Medium temperature | -20…90 °C | -10…140 °C | 0…50 °C | 0…50 °C | 0…50 °C |
 | Local display | ❌ No | ❌ No | ✅ Yes | ✅ Yes | ❌ No |
 | Max pressure | 10 / 16 bar(g) | 12 bar(g) | 10 bar(g) | 10 bar(g) | 16 bar(g) |
 | Price | from € 550,- | from € 195,- | from € 799,- | from € 1.330,- | from € 1.250,- |
| Product page | View MAG-VIEW | View LIQUI-VIEW | View MASS-VIEW | View MASS-STREAM | View FLEXI-FLOW | |
Not sure which type fits your application? Get free advice from our specialists →
Which flow meter type fits your application?
Each measurement principle has its own strengths. Below you can read when to use each type, how it works, and when to choose another type instead.
When should you use a magnetic flow meter?
Use a magnetic flow meter for conductive, water-based liquids above 20 µS/cm, such as tap water, cooling water and water-glycol mixtures. A magnetic flow meter has no moving parts and no obstructions in the flow path, so it needs little maintenance and causes virtually no pressure loss.
Several of our models (MVM-005-QA, MVM-001-Px, MVM-002-Px, MVM-030-Px) have a narrowed section in the flow path. This increases the flow velocity and improves accuracy at low flow rates.
How does a magnetic flow meter work?
A magnetic flow meter is based on Faraday's Law of Electromagnetic Induction. In 1831, Michael Faraday observed that a voltage is induced across a conductor moving at right angles through a magnetic field, and that this voltage is proportional to the conductor's velocity.
In the meter, an iron-core permanent magnet creates a magnetic field across the full cross-section of the pipe. The conductive liquid flows through this field at a 90-degree angle. The induced voltage is proportional to the flow velocity, and therefore to the flow rate.
Want to know more? Read how a magnetic flow meter registers water flow.
When should you use a vortex flow meter?
Use a vortex flow meter for a cost-effective measurement of water-like liquids, both conductive and non-conductive, including deionized water. The LIQUI-VIEW Base starts at €195 and can be mounted in any position.
How does a vortex flow meter work?
An obstruction in the flow (the bluff body) sheds vortices downstream at a frequency proportional to the liquid velocity. A piezoelectric sensor detects these vortices and converts them into electrical pulses proportional to the flow rate.
LIQUI-VIEW Base provides a frequency or analog (4–20 mA) output. The analog version can be equipped with a bright, wide-angle display that rotates through 180 degrees, so it stays readable in every mounting position.
When should you use a thermal mass flow meter?
Use a thermal mass flow meter for gases such as compressed air, nitrogen, argon, CO₂, helium and hydrogen. It measures mass flow directly, so you do not need separate pressure and temperature compensation.
How does a thermal mass flow sensor work?
A small heater warms the flowing gas while a temperature sensor measures the heat carried away. The higher the gas flow, the more heat is carried away. The electronics supply extra energy to keep a constant temperature difference (ΔT). That energy is a direct measure of the gas mass flow rate.
What is Constant Temperature Anemometry (CTA)?
MASS-VIEW and MASS-STREAM use Constant Temperature Anemometry (CTA), also called the direct through-flow principle. Unlike bypass-based meters, the gas flows directly over the sensor without being diverted. The sensor has two probes:
- A heater that adds heat to the gas
- A temperature sensor that measures the gas temperature
The electronics keep the temperature difference between the two probes constant. As the gas flow increases, more power is needed to maintain it. That heater power gives a direct indication of the gas mass flow rate.
What is MEMS-based thermal mass flow measurement?
FLEXI-FLOW Compact uses a compact MEMS-based thermal sensor, with tiny heating elements and temperature sensors directly in the flow channel. MEMS technology lets one device measure mass flow, temperature and pressure, with ± ~1% accuracy and Bluetooth connectivity.
MASS-VIEW, MASS-STREAM or FLEXI-FLOW: which one do you need?
- MASS-VIEW: the digital alternative to a variable area flow meter (rotameter), with a built-in display. Ideal when you want a clear local readout of gas flow. From €799.
- MASS-STREAM: an inline thermal mass flow meter with display and 4–20 mA / RS-232 output, for monitoring gas consumption. From €1,330.
- FLEXI-FLOW Compact: the smart choice when accuracy (± ~1%), digital integration (Modbus-RTU, FLOW-BUS) and extra pressure and temperature data matter. Up to 16 bar(g). From €1,250.
Frequently asked questions about choosing a flow meter
What flow meter do I need for gas?
For gases, choose a thermal mass flow meter. It measures mass flow directly, so the reading does not depend on pressure or temperature changes. Choose MASS-VIEW for a local display, MASS-STREAM for inline monitoring, or FLEXI-FLOW for the highest accuracy and digital integration.
Which flow meter is best for liquids?
For conductive water-based liquids above 20 µS/cm, a magnetic flow meter is best: no moving parts and virtually no pressure loss. For non-conductive liquids such as deionized water, choose a vortex flow meter.
Can a magnetic flow meter measure deionized water?
No. A magnetic flow meter needs a conductivity above 20 µS/cm. Deionized water is below that, so use a vortex flow meter such as LIQUI-VIEW.
Which flow meter is best for compressed air?
A thermal mass flow meter. It measures air consumption in mass units (ln/min) and helps detect leaks. MASS-STREAM is suitable up to 10 bar(g), and FLEXI-FLOW up to 16 bar(g).
What is the difference between mass flow and volume flow?
Volume flow (l/min) changes with gas pressure and temperature; mass flow (ln/min or kg/h) does not. That is why gases are usually measured as mass flow, and water-like liquids as volume flow.
How do I choose a flow meter based on flow range?
Determine your minimum, normal and maximum flow. Choose a meter whose range covers all three, with the normal flow roughly in the middle of the range. Measuring at the very bottom of the range reduces accuracy.
How accurate is a thermal mass flow meter?
The thermal mass flow meters in our range reach ± 1.5% (MASS-STREAM), ± 2% (MASS-VIEW) and ± ~1% (FLEXI-FLOW).
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