Enter all but one of the discharge coefficient, density of the fluid, cross-sectional area of the orifice, and velocity of the fluid into the calculator to determine the pressure drop across the orifice; this calculator can also evaluate any of the variables given the others are known.

Orifice Pressure Drop Formula

The following formula is used to calculate the pressure drop across an orifice:

Q = Cd * A * sqrt(2 * g * h)


  • ΔP is the pressure drop across the orifice
  • C is the discharge coefficient of the orifice
  • ρ is the density of the fluid
  • A is the cross-sectional area of the orifice
  • V is the velocity of the fluid

To calculate the pressure drop across the orifice, multiply the discharge coefficient by the density of the fluid, the cross-sectional area of the orifice, and the square of the velocity of the fluid. Divide the result by 2.

What is an Orifice Pressure Drop?

An orifice pressure drop refers to the reduction in fluid pressure that occurs when the fluid flows through an orifice or a constriction in the pipe. This phenomenon is commonly used in engineering applications to measure the flow rate of the fluid. The principle behind this is Bernoulli’s equation, which states that the sum of the pressure energy, kinetic energy, and potential energy in a fluid remains constant. When the fluid passes through the orifice, its velocity increases, leading to an increase in kinetic energy. To maintain the energy balance, the pressure energy decreases, resulting in a pressure drop. The magnitude of this pressure drop can be calculated using the orifice equation, which takes into account the diameter of the orifice, the diameter of the pipe, the fluid density, and the fluid velocity. This pressure drop is then used to determine the flow rate of the fluid.

How to Calculate Orifice Pressure Drop?

The following steps outline how to calculate the Orifice Pressure Drop:

  1. First, determine the upstream pressure (P1) and downstream pressure (P2) in psi.
  2. Next, determine the orifice diameter (d) in inches.
  3. Next, gather the formula from above = ΔP = P1 – P2.
  4. Finally, calculate the Orifice Pressure Drop.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

upstream pressure (P1) = 100 psi

downstream pressure (P2) = 80 psi

orifice diameter (d) = 0.5 inches