How to Calculate Flow Rates

••• faucet image by Lynne Davis from

The flow rate is the rate at which a liquid moves through a channel, such as water moving through a faucet. Flow can be smooth or rough, fast or slow, depending on the characteristics of the channel and liquid. Liquids flow due to gravity and pressure, and this flow rate can be measured using a formula. Knowing the flow rate of a liquid is important for things such as creating irrigation systems, sprinkler systems and choosing a pipe size.

    Hook a 25 mm plastic tube onto the open end of the pressure gauge.

    Hook the pressure gauge onto your liquid source (such as a water faucet).

    Turn on the tested gate valve by twisting it counter-clockwise. This will cause the water to run out and through the clear plastic tubing.

    Turn off the tested gate valve when the meter reads "240kPa," which is the standard pressure used for irrigation systems.

    Hold the clear plastic tubing above the 9 liter bucket and allow the water to flow into the bucket. At the same time, press "Start" on a stopwatch. Calculate how long it takes for the water to fill the bucket to the top. Press "Stop" on the stopwatch when the water reaches the top. Write down the number of seconds it took to fill the bucket.

    Use this formula to find the flow rate: Liters x 60 / seconds. For example, 9 liters x 60 = 540 / seconds = flow rate.


About the Author

Susan Reynolds has been a writer since 2008. She holds a B.A. in English from the University of South Florida and is a licensed real estate agent in Florida.

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