The mass flow rate of a system is a measurement of how much mass of a given material passes through a defined plane of space in a given time period. It is typically expressed in units like pounds per hour. Mass flow is related to volumetric flow, which is a measurement of the volume of a material that passes through a plane. It is usually expressed in units like gallons per minute. If you have a measurement of the specific gravity of the material in question, it is possible to convert the former to the latter.
Things You'll Need
 Calculator
 Mass scale

Calculate the specific gravity of the material you are measuring, if you do not have it already. Specific gravity of a liquid is a measure of the ratio of the mass of a given volume of your material to the mass of an equivalent volume of water. Both measurements can be made with a mass scale.

Multiply the specific gravity by 500.

Divide your pounds per hour measurement by the result calculated in Step 2 to find the equivalent measurement of gallons per minute.
References
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