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Gas Orifice & Choke Flow Calculator

Subcritical and critical gas flow through an orifice — Mscf/d screening.

Gas flow through an orifice or choke — subcritical and critical (choked) regimes. Useful for surface facility and wellhead choke screening (Mscf/d, field units).

Upstream pressure P1 (psia)

Downstream pressure P2 (psia)

Orifice diameter (in)

Discharge coefficient Cd

Temperature (°F)

Gas specific gravity γg

Compressibility Z

Isentropic exponent k

Results

Gas rate

775 Mscf/d

Flow regime

Critical (choked)

Pressure ratio P2/P1

0.125

Critical ratio

0.549

Critical (choked) flow ≈ 775 Mscf/d — downstream pressure below critical ratio 0.549. Calibrate Cd to facility data; multiphase orifice needs dedicated correlations.

engineeringEngineering screening only. Engineering screening calculator only — not a substitute for licensed professional engineering, API/ASME/code-compliant design, certified reserves audits, regulatory well approvals, or field-measured PVT and flow data. Verify all inputs, units, and correlations against your facility standards and qualified sign-off before operations or design decisions.

Need expert help?

Build facility choke models in Spreadsheet Studio

Multistage choke schedules, allocation, and sensitivity tables — Caleb in Workspace for completion & surface network memos when signed in.

psychologySpecialist: Caleb — Petroleum Engineer

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Chokes hide in plain sight on every wellhead

Orifice and choke equations bridge upstream pressure, downstream backpressure, and deliverability. Critical flow occurs when downstream pressure drops below the critical ratio — rate then depends only on upstream conditions.

Discharge coefficient and Z-factor dominate uncertainty. Calibrate to measured rates whenever possible.

Use this for facility screening; multiphase choke correlations need dedicated models in Spreadsheet Studio or specialist software.

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