Fluid Flow Fundamentals

Water systems involve the movement of water from one point to another. Examples are transferring water from one process to another, or from one production facility or building to a packaging plant or final product shipping area.

Water usage is typically expressed as a volumetric flow rate (volume/time). If the water flowing though a cylindrical pipe is represented by the shaded area shown below (perpendicular to flow direction) and the velocity of the water is known, then the flow rate of the water can be determined through the pipe as gal/min or m3/sec.

Flow Rate Calculator
Velocity =
Cross Sectional Area =
Flow Rate =
SI Calculator
Velocity =
Cross Sectional Area =
Flow Rate =

Flow Rate Equations

Flow Rate (Q) = Area x Velocity

The flow rates of process pipes are very important to know to complete water balances and usage and measuring volumetric flow rates are easy using common flow meters. See Types of Flow Meters for various types of flow measurement devices.

Sample Calculation: Determine the quantity of water flowing through a 6-inch diameter pipe that has a velocity of 5 ft/sec.

Flow rate (cfs) = Velocity (ft/sec) x Pipe Cross Sectional Area (ft2)
Flow rate (cfs) = 5 ft/sec x .196 ft2
Flow rate (cfs) = 0.98 ft3
Multiply 0.98 ft3 By 449 to get gpm
Flow (gpm) = 0.98 x 449
= 440 gpm

SI Units

Flow M3 / S = Velocity (m/s) x Pipe Cross Sectional Area (m2)
Flow M3 / S = 1.52 m/s x .018 m2
= .028 m3/sec
Multiply 0.028 m3 /sec by 1000 to get L / S
Flow L / S = 0.028 x 1000
Flow L / S = 28 L / S



Other Helpful Calculators

To print this calculator or to use it as a standalone file, please download the Excel format below. (Right-click on the link and select "Save Target As" to download it to your computer.)

Download Excel format


L/S = Liters per Second
gpm = Gallons per Minute
HP = Horsepower
KW = Kilowatt
m/s = Meters per Second
= Cubic Meters
= Square Meters
ft² = Square Feet
ft³ = Cubic Feet


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