Use the calculator to estimate gas flow through an orifice/choke (choked or subcritical), size an orifice for a target flow, or estimate wellhead choke rate using a simple sonic-flow correlation. Choose a tab, enter the requested values, then click Calculate.

Choke Coefficient Calculator

Tools for choked/subcritical gas flow through an orifice or choke. Choose a tab, enter values, then Calculate.

Orifice Flow
Size Orifice
Wellhead Choke

Related Calculators

Choke Coefficient Formula

There is no single universal “choke coefficient” that can be calculated as a simple ratio like flow divided by pressure drop. In practice, different coefficients are used depending on the correlation and regime. The “Wellhead Choke” tab uses an empirical sonic-flow correlation of the form below (with units as stated in the calculator).

Q_{scfd} = K\,C_d\,P_1\,d^2
K = \frac{Q_{scfd}}{C_d\,P_1\,d^2}

Variables:

  • Qscfd is the standard volumetric gas rate in standard cubic feet per day (scf/d)
  • K is a correlation constant (its numeric value depends on the chosen correlation and the units used)
  • Cd is the discharge coefficient (dimensionless)
  • P1 is the upstream absolute pressure (psia in the calculator’s correlation)
  • d is the choke/orifice diameter (inches in the calculator’s correlation; “64ths in” is converted to inches internally)

If you have measured (or specified) a standard flow rate and want the correlation constant, rearrange the equation to K = Qscfd/(CdP1d²). Note that K is not dimensionless in this form because it depends on the selected units.

What is a Choke Coefficient?

“Choke coefficient” is a general term used for a parameter that relates flow rate to upstream conditions and choke size for a particular choke model or correlation. Depending on the application, this may refer to:

  • a discharge coefficient (Cd) used with orifice/nozzle flow equations (dimensionless), and/or
  • an empirical correlation constant (K) used in a simplified wellhead choke rate equation (units depend on how the equation is written).

Because the definition depends on the chosen model and units, it’s important to use the coefficient in the same way it was defined or calibrated.

How to Calculate Choke Coefficient?

The following steps outline how to calculate a choke correlation constant K from the wellhead choke equation.

  1. Determine the upstream absolute pressure P1 (for example, psia).
  2. Determine the choke/orifice diameter d and ensure it is in the correct units for the correlation (the calculator converts “64ths in” to inches).
  3. Choose a discharge coefficient Cd (dimensionless) consistent with your choke type.
  4. Determine the standard flow rate Qscfd (scf/d).
  5. Calculate K = Qscfd/(CdP1d²), or use the “Wellhead Choke” tab by entering K and solving for Q.

Example Problem : 

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

Upstream pressure (P1) = 500 psia

Choke size = 20/64 in (d = 0.3125 in)

Discharge coefficient (Cd) = 0.60

Standard flow rate (Qscfd) = 1,200,000 scf/d

Compute the correlation constant:

K = Qscfd/(CdP1d²) = 1,200,000 /(0.60 × 500 × 0.3125²) ≈ 40,961