How to calculate differential pressure levels

Written by heather robson
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How to calculate differential pressure levels
Measuring differential pressure uses a complex equation. (pressure image by Pavel Vlasov from

Differential pressure is a measurement used in liquid systems to calculate the differences in pressure at different points within the system. For example, a plumber may need to calculate the difference in pressure levels at different points along the route that water travels within a home's pipes. A number of factors affect the final value for the differential pressure. It's a more complicated calculation than simply measuring the pressure of the system at two points and subtracting.

Skill level:

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Things you need

  • Pressure gauge
  • Calculator

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  1. 1

    Determine the change in pressure between the two points in the system. You will need an instrument such as a pressure gauge to determine the pressure at two points. Subtract the smaller number from the larger. Call this value "P".

  2. 2

    Measure the diameter of the pipe that the liquid travels through. Call this value "d".

  3. 3

    Determine the density of the fluid that you are measuring. Call this value "p".

  4. 4

    Determine the rate of flow of the liquid, also known as the mass flow rate. Call this value "W".

  5. 5

    Calculate the differential pressure using the following equation: K = (1.59923 x P x (d^4) x p)/(W^2)

  6. 6

    Calculate "d" to the fourth power and multiply the answer by P x p x 1.59923.

  7. 7

    Calculate the square of "W".

  8. 8

    Divide the answer in step 6 by the answer in step 7 to determine the differential pressure.

Tips and warnings

  • Differential pressure gauges are available. These gauges monitor the pressure at two points and automatically calculate and update the differential pressure before displaying it on a single dial, making them much easier and more practical to use than doing the calculation manually.

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