How do you convert PSI water pressure to gallons per minute?


You cannot directly convert PSI to GPM. They are two different units of measure. PSI measures pressure, and GPM measures flow rate. However, if other variables are known, you can use Bernoulli's equation to indirectly make a conversion. The following assumes the flow is in a pipe and the pipe diameter is known. It also assumes a steady state incompressible flow.

  1. Ensure all units agree

    Ensure all units to be used agree with each other. This means ensuring there are no variables given in metric and that everything is measured in inches, not feet.

  2. Use Bernoulli's equation to determine fluid velocity

    Use this equation, (g*h + (P/rho) + (V^2/2)) = constant, to solve for velocity. Upon isolating velocity, the equation will look like this: V = sqrt(2 * ((-P/rho) - g * h)) where P is the pressure, rho is the density of the fluid, g is gravity and h is the elevation above the reference plane.

  3. Determine the flow rate

    Using the equation Q = V * A, calculate the velocity. Q is the volumetric flow rate, V is the velocity of the fluid and A is the cross-sectional area of the pipe.

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