What is the difference between actual and standard volumetric flow?

Actual volumetric flow (ACFM or m³/h) is the volume of gas moving per unit time at the actual pressure and temperature in the pipe. Standard volumetric flow (SCFM or Sm³/h) is the equivalent flow referenced to standard conditions (14.696 psia / 60 °F in the US, or 101.325 kPa / 15 °C in SI). Standard flow is used for billing, equipment sizing, and comparing flows at different operating conditions.

What standard conditions does this calculator use?

For US units, standard conditions are 14.696 psia (1 atm) and 60 °F (520 °R). For metric units, standard conditions are 101.325 kPa and 15 °C (288.15 K). These are the most common standards for natural gas and compressed air applications.

Why does the calculator use absolute pressure?

The ideal gas law and all compressible flow equations require absolute pressure. Absolute pressure = gauge pressure + atmospheric pressure. For US units, add 14.696 psi to your gauge reading. For metric, add 101.325 kPa to your gauge reading.

Is this accurate for real gases at high pressure?

This calculator uses the ideal gas law, which is accurate for most gases at moderate pressures (below about 200 psia or 1.4 MPa) and temperatures well above the critical temperature. At very high pressures or near the gas critical point, a compressibility factor (Z-factor) correction should be applied. For high-pressure natural gas pipelines, use a dedicated compressible flow tool.

What is a good gas velocity limit for pipes?

Recommended maximum gas velocities depend on the application. For dry natural gas, 50–80 ft/s (15–24 m/s) is typical in distribution. For compressed air headers, 20–30 ft/s (6–9 m/s) is recommended to minimize pressure drop. Velocities above 100 ft/s (30 m/s) in carbon steel pipes can cause erosion, especially if the gas contains particulates or liquids.

Gas Flow Rate Calculator

Enter pipe diameter, pressure, temperature, and gas type to calculate volumetric and mass flow rates in standard and actual conditions.

Gas Flow Inputs

Unit System

Gas Type

Pipe Inside Diameter

Pipe Length

Upstream Absolute Pressure (inlet)

psia

Downstream Absolute Pressure (outlet)

psia

Gas Temperature

°F

Fill in the inputs and click Calculate
to see volumetric and mass flow rates.

Summary

This gas flow rate calculator uses the ideal gas law and Darcy-Weisbach equation to compute volumetric and mass flow rates of gases through circular pipes. Enter the pipe geometry, upstream and downstream pressures, temperature, and select a gas type to get actual volumetric flow (ACFM or m³/h), standard volumetric flow (SCFM or Sm³/h), and mass flow rate (lb/hr or kg/hr). All calculations run entirely in your browser.

How it works

Select your unit system: US customary (psi, °F, inches) or metric (kPa, °C, mm).
Choose the gas type, or select "Custom" to enter a molecular weight.
Enter the pipe inside diameter and length.
Enter the upstream (inlet) absolute pressure and downstream (outlet) absolute pressure.
Enter the gas temperature.
Click Calculate to see actual volumetric flow, standard volumetric flow, mass flow rate, velocity, and Reynolds number.

Use cases

Sizing natural gas supply lines for industrial burners and boilers.
Calculating compressed air flow through distribution piping.
Verifying that a gas pipeline can handle a required flow capacity.
Converting between actual and standard volumetric flow conditions.
Estimating mass flow rate for combustion and process engineering calculations.
Checking gas velocity against maximum allowable limits to prevent erosion.
Teaching fluid mechanics and ideal gas law concepts in engineering courses.
Designing HVAC ventilation and exhaust systems.

Frequently Asked Questions

Last updated: 2026-05-28 · Reviewed by Nham Vu