For petroleum engineers, plumbers and rocket scientists, mass flow rate calculations are part of daily practice.

    Some might even consider them intuitive, as guessing what size drain is needed for your new swimming pool is generally not an advanced mathematical problem.

    When working with mass flow rate, you'll likely encounter many different measurement units. For help with conversions, try our free mass flow rate calculator. This handy tool converts between 50+ units and rounds up to six decimal places.

    Have questions about about mass flow rate? Read on to learn more.


    What is mass flow rate?

    If you are moving a fluid from one place to another, you need to understand the mass flow rate.

    The mass flow rate of a system is the mass of a fluid passing a point in the system per unit of time. Fluids can be liquids or gas.

    This could be tons of crude oil in a day pumped out of a well, kilos of chlorine gas per second or even pounds of chocolate pudding per minute.

    In physics and engineering, mass is the volume an object occupies multiplied by the density of the object.

    For fluids, the density, volume, and shape of an object all can change in the system with time.

    Mass flow rate is often confused with volumetric flow rate, but these are different types of measures.

    What is the standard unit of mass flow rate?

    The SI for mass flow rate is kilogram per second (kg/s). While the U.S. customary unit is pound per second (lb/s).

    The common symbol is an m with a dot over it to indicate that this is a time derivative. It can also be symbolized by the lowercase Greek letter mu (μ).

    What is the formula for mass flow rate?

    There are a few different equations that can be used for mass flow rate.

    For a Flat, Plane Area

    m = r · V · A


    • m is Mass Flow Rate
    • r is the density of object
    • V is the velocity of object
    • A is the area of cross section

    For the purposes of problem-solving, r, V and A are constant and there is no friction. Mass is always conserved.

    So, if a fluid water enters a pipe at 1 kg/s it must leave the pipe at 1 kg/s.

    At Stp Conditions

    Sometimes, mass flow rate is related to volumetric flow rate. At stp conditions, the formula for mass flow rate is:

    m = r · Q


    • r is the density of object
    • Q is the volume of object (m3)

    Other Formulas

    It can also be expressed as a calculus equation (a limit) or a surface integral equation (for curved surfaces).

    How do you convert mass flow rate?

    Mass flow rate is typically measured in kilograms/seconds, but there are a slew of other units you may have to work with.

    Examples include pounds per second, milligrams per minute and more.

    If you need to change your unit of measure, it's best to use our mass flow rate converter.

    You could still convert by hand if you have the time and know the right ratios to use. But even so, it's a good idea to check your work with a good conversion calculator.

    Example: Lb/h to Kg/s

    Let's convert 2 pounds per hour to kilograms per second.

    2 pounds = 0.907185 kilograms

    1 hour = 3600 seconds

    = 0.907185 / 3600

    = 0.000252 kilogram/second

    We hope these hints and our easy mass flow rate converter are useful to you. Save the conversion calculator to the home screen of your smartphone, for quick access to it.

    How do you measure mass flow rate?

    In a practical context, a flowmeter measures the amount of fluid movement from one point to another.

    There are three types of flowmeters commonly used. They are:

    1. Differential Pressure Flow Meter

    A pipe is blocked by a membrane of known thickness with an opening of known size. The fluid pressure is measured on each side.

    The difference in the reading of one side of the blockage to the other is proportional to the distance between the two points.

    The volumetric flow rate, viscosity of the fluid, and the diameter of the vessel (pipe), must be known.

    Corrections are then made for temperature and pressure to produce a mass flow rate.

    2. Thermal Mass Flow Meter

    These derive mass from the specific heat capacity of the fluid. The specific heat capacity of the fluid must be given.

    Some or all of the flow passes through a tube. An amount of heat is applied to the tube. The change in temperature is observed.

    The difference in temperature between the two points indicates the amount of the fluid's energy absorption, which is dependent on the mass moving through the tube.

    3. Coriolis Mass Flow Meter

    A Coriolis mass flow meter measures mass through inertia. Fluid flows through a vibrating tube.

    This movement produces a twisting force proportional to the mass.

    The mass flow rate is measured without needing to know the density, specific heat capacity or other knowledge of the fluid flowing inside.

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