1. Gas and operating conditions

Known flow basis

Known flow rate

Known flow unit

Gas / mixture

Molecular weight (g/mol)

For mixtures, use the mole-fraction-weighted molecular weight.

Operating pressure

Operating pressure unit

Local atmospheric pressure (kPa absolute)

Used only for gauge pressure conversion.

Operating temperature

Operating temperature unit

Operating compressibility factor, Z

Z = 1 assumes ideal gas behavior. Enter a suitable real-gas value when needed.

2. Define the reference conditions

“Standard” flow has no single universal temperature. Match the reference basis used by your supplier or meter.

Reference conditions

Reference temperature (°C)

Reference pressure (kPa absolute)

Reference compressibility factor, Z

Gas flow results

Enter conditions and calculate.

Calculation basis

ρ = P M / (Z R T)
ṁ = ρ_actual Q_actual = ρ_reference Q_reference
Q_reference / Q_actual = (P_actual / P_reference) × (T_reference / T_actual) × (Z_reference / Z_actual)

Internally, pressures are absolute Pa, temperatures are K, molecular weight is kg/mol, and R = 8.31446261815324 J/(mol·K). Gauge pressure is converted using the entered atmospheric pressure.

Use for a single gas phase with unchanged composition between operating and reference conditions. Gas presets set molecular weight only; they do not calculate Z, humidity, phase equilibrium, or condensation. Enter compressibility values appropriate to both states. Standard volume is a bookkeeping basis, not a promise that the gas remains gaseous at that state.

This tool converts a known flow. It does not predict flow from pipe pressure drop or calculate choked flow. For a valve flow calculation, use Gas Control Valve Sizing.

Gas Flow Calculator