Mass flow rate vs Volumetric flow rate is what we must use in flow measurement and control. In this post, we compare the concept of volume flow and mass flow and the conversion between the two.

Mass Flow Rate vs Volumetric Flow Rate

Commonly used flow meters, such as orifice plates. Turbine flowmeter. Vortex flowmeter. Electromagnetic Flowmeter. Rotameter. The flow measurement value of ultrasonic flowmeter and oval gear flowmeter is the volume flow of fluid. Coriolis mass flow meters and thermal gas mass flow meters measure mass flow.

Sino-Inst offers a variety of volume flow and mass flow meters for flow measurement. If you have any questions, please contact our sales engineers.

What is Flow Rate?

Flow rate refers to the ratio of the amount of fluid flowing through the cross-section of the pipe to the time it takes for that amount to pass through the cross-section. Flow is divided into volume flow and mass flow.

What is volume flow?

The volume flow rate is the flow rate expressed by the volume of the fluid quantity.
The volume flow is expressed by the formula: qv=V/t=u×A.
In the formula: qv is the volume flow, m3/s.
V is the unit flow volume, m3.
t is the unit time, s.
u is the average flow velocity in the pipe, m/s.
A is the cross-sectional area of ​​the pipeline, m2.

Among the commonly used flow meters, such as orifice plates, turbine flow meters, vortex flow meters, electromagnetic flowmeters, rotameters, ultrasonic flow meters, and oval gear flow meters, the flow measurement value is the volume flow of the fluid.

Featured Volume Flow Meters

What is mass flow?

Mass flow rate refers to the flow rate of fluid quantity expressed by mass.
The mass flow rate can be expressed by the formula: qm=m/t=ρ×u×A.
In the formula, qm is the mass flow rate, kg/s.
m is the unit fluid mass, kg.
ρ is the fluid density, kg/m3.
t is the unit time, s.
u is the average flow velocity in the pipe, m/s.
A is the cross-sectional area of ​​the pipeline, m2.

Extended reading: Gas mass flow controller working principle

Featured Mass Flow Meters

Volumetric flow rate to Mass flow rate

  1. If the mass flow of the flow is known and needs to be converted into volume flow, the following formula can be used: qv=qm/ρ. In the formula, qv is volume flow, m3/s. qm is mass flow, kg/s. ρ is fluid Density, kg/m3.
  2. If the volume flow rate of the fluid is known, it needs to be converted into a mass flow rate, which can be done with the formula: qm=qv×ρ.

How to convert air volume flow to air mass flow?

The conversion factor between air volume flow rate and air volume flow rate is 1.29. That is, to convert the volume flow of air into the mass flow, multiply the coefficient by 1.29.

Solution: Let the mass of air passing in t hours be m kg, the volume be V cubic meters, and the known air density ρ = 1.29 kg/m3.

Then the volume flow rate of the air qv=V/t (cubic meters/hour), and the mass flow rate qm=m/t (kg/hour).

And because air quality = air density x air volume, m = ρV = 1.29V.

Then qm=m/t=ρV/t=ρqv=1.29qv.

That is, to convert the volume flow of air into a mass flow, multiply the coefficient by 1.29.

Converter Tool: Volumetric Flow Rate & Pipe Diameter to Flow Speed Calculator

Density, Mass Flow, and Volumetric Flow

A description of the relationship between density, mass flow rate, and volumetric flow rate. The following video provides a good explanation.

Video source:

Volume flow unit converter

UnitL/minm3/hf t 3/hUkgal/minUsgal/minUS  bbl/d

mass flow rate units converter

1 kilogram per second (kg/s)

=3600.0000 kilograms per hour (kg/h)

=3.6000 tons per hour (t/h)

=86.4000 tons per day (t/d)

=2.8800×104 tons per year (t/a)

= 2.2046 pounds per second (lb/s)

= 7936.6414 pounds per hour (lb/h)

= 1.9048 x 105 pounds per day (lb/d)


mass flow rate and pressure relation

In theory, mass flow is not affected by pressure. It only depends on the geometry of the measuring tube and the oscillatory behavior of the measuring system.

In practice, however, changes in the working pressure cause changes in the geometry of the measuring tube and affect the oscillation characteristics of the measuring system. resulting in measurement errors.

At this point, we have used the experimental method to confirm the influence of the change of the working pressure on the measurement accuracy of the flowmeter.

We found that the actual working pressure of the flowmeter will produce an additional error of -0.12 to -0.17% for every 0.1Mpa increase in the flowmeter. That is, when the working pressure is higher than the verification pressure, an additional error of about -0.15% will be generated for every 0.1Mpa higher than the flowmeter.

And when the working pressure is lower than the verification pressure. Every low 0.1Mpa flow meter will produce an additional error of about +0.15%.

This experimental data is basically consistent with our mass flow meter data (-0.13%/0.1Mpa).

How to reduce the effect of pressure on the mass flow meter?

In order to avoid the influence of pressure changes on the measurement accuracy of the flowmeter in practical applications, the following methods can be taken:

  1. When selecting a model, try to use a mass flowmeter that is less affected by pressure changes;
  2. On-line verification of the flowmeter. When the conditions for online verification are not available, the flowmeter should also be verified offline under working pressure.
  3. The flowmeter is relatively stable for some additional errors caused by the influence of pressure. The real-time pressure compensation calculation can be realized by means of software by installing a pressure transmitter.


If the volume flow rate of the fluid is known, it needs to be converted into mass flow rate, which can be carried out by the formula: qm=qv×ρ

Volume flowrate (Volume Flowrate) is the volume of fluid passing through the flow section per unit time, referred to as flow rate, expressed by Q.
Flow rate expressed in volume/time or volume/time. Such as: m³/h ,l/h.
Volume flow rate (Q) = average velocity (v) * pipe cross-sectional area (A)

The fluid pressure and flow rate in the pipeline are completely two concepts. For fluids with high pressure, the flow rate can be high or low.
Engineering pressure is the amount of force per unit area. The flow rate is the amount (weight or volume) of the fluid flowing through the pipe per unit time.
Here, there is another important parameter: flow rate. It is the average velocity of fluid flowing in the pipe. The unit is: the flow rate per unit area (internal section of the pipeline). That is: the flow rate multiplied by the pipe cross-sectional area equals the flow rate.
If the fluid is a gas (compressibility), the flow rate is constant, and the flow rate of a gas with high pressure is of course also large. If the size of the pipe is constant, the flow rate of the fluid with a large flow rate is of course also large; the pressure loss (i.e. pipeline resistance) is proportional to the square of the flow rate, that is, proportional to the square of the flow rate.
If the fluid under a certain pressure is directly discharged to the atmosphere under certain conditions (the diameter of the pipe is the same), the fluid pressure can be converted into velocity energy, and the flow rate of the fluid with high pressure is correspondingly high, and of course, the flow rate is also large.

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Mass Flow Rate vs Volumetric Flow Rate

Sino-Inst is Manufacturer of Mass Flow Meters and Volumetric Flow Meters. We supply more than 50 kinds of Flow Meters. 40% mass flowmeters, and other types of Volumetric flowmeters.

Since the mass flowmeter has the ability to directly measure the mass flow of fluid beads, the measurement accuracy is high. It has a wide range of applications, low installation requirements, reliable operation of the instrument, and low maintenance rate. Mass flow meters have been widely used in flow measurement in petroleum, chemical, metallurgy, thermal, electric power, food and other fields.

Volumetric flowmeters are low cost and cover more measurement applications. It is also widely used in various industrial production control processes.

Sino-Inst’s Mass Flow Meters and Volumetric Flow Meters, made in China, Having good Quality, With better price. Our flow measurement instruments are widely used in China, India, Pakistan, the US, and other countries.

The entire team at Sino-Inst’s has received excellent training, so we can ensure that every client’s needs are met. For assistance with your product requirements, whether it’s a flow sensor, level sensor, or other device, give us a call.

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