Gas Flow Converter
Convert gas flow between actual, normal, standard, and mass flow units. On the input side a unit is just a scale and the conditions carry the state: enter SCFM as ft³/min with the US standard preset, or Nm³/h as m³/h with the Normal (DIN 1343) preset — the reference conditions are what most conversions get wrong.
Flow Input
All Conversions
Actual — at line conditions
m³/h (actual)
13.5705
m³/min (actual)
0.226175
L/min (actual)
226.175
ACFM
7.98731
Normal — 0 °C / 101.325 kPa (DIN 1343)
Nm³/h
100
Nm³/min
1.66667
Nl/min
1,666.67
Standard
Sm³/h
105.491
SCFM
62.0899
SCFH
3,725.4
Mass flow
kg/h
129.223
kg/s
0.0358953
lb/h
284.888
lb/min
4.74813
How the Conversion Works
Converting a gas flow from one reference condition to another is an ideal-gas volume correction. The same mass of gas occupies a different volume at each temperature and pressure:
Mass flow is the condition-independent quantity, so this converter works through it: the volumetric flow is multiplied by the gas density at its own reference condition, and the result is re-expanded at every other condition. Density follows from the ideal gas law with M the molecular mass:
All pressures are absolute. The converter assumes ideal-gas behaviour (Z = 1), which is accurate for reference-condition conversions and low-pressure lines; at high line pressures the actual-flow figures deviate by the gas's compressibility factor.
Reference Conditions Compared
"Standard" conditions are not standardised — the same SCFM label can mean different reference states depending on the industry. Always check which definition your instrument, datasheet, or contract uses.
| Name | T | P (abs) | Typical use |
|---|---|---|---|
| Normal (DIN 1343) | 0 °C | 101.325 kPa | Nm³/h, Nl/min — European process and instrumentation |
| Standard (ISO 13443) | 15 °C | 101.325 kPa | Sm³/h — natural gas, international |
| Standard (US) | 60 °F | 14.696 psia | SCFM, SCFH, MMSCFD — US oil and gas |
| US pipeline (AGA) | 60 °F | 14.73 psia | Gas measurement contract base (state bases range 14.65–15.025 psia) |
| ISO 1217 / ISO 6358 | 20 °C | 100 kPa | Compressor ratings (CAGI, dry air) and pneumatics ANR |
| NTP | 20 °C | 101.325 kPa | Laboratory and ventilation contexts |
Inputs and outputs explained
- Input value, unit and conditions. The unit you enter is a pure scale (m³/h, CFM, kg/h …); the temperature and pressure fields say what state that volume is at. "100 Nm³/h" (normal cubic metres) is entered as 100 m³/h with the Normal preset, "100 SCFM" (standard cubic feet per minute) as 100 ft³/min with the US standard preset, and a flow meter reading as its own line temperature and absolute pressure. Pressures are absolute; a gauge unit has the standard atmosphere, 1.01325 bar, added.
- Gas and molecular mass M. M sets the density through the ideal-gas law and therefore the mass flow; it cancels out of any volume-to-volume conversion (Nm³/h ↔ Sm³/h ↔ actual), which is why those results do not change when you switch gas. The natural-gas preset, 17.4 g/mol, is a typical pipeline-quality value — real gases run from about 16 (lean) to 19 g/mol (rich); use Custom with your gas analysis.
- Result sections. Normal (Nm³) is fixed at 0 °C / 101.325 kPa (DIN 1343). Standard (Sm³, SCF) is whichever reference state you pick — the table above shows why the choice matters by up to 7 %. Actual (ACFM, m³/h actual) is the volume the gas really occupies at the line temperature and pressure you set in that section; ANR is the pneumatics term for the ISO 6358 reference atmosphere.
- Mass flow. The condition-independent quantity every conversion passes through: value → kg/s at the input state → each output state. It is also what the SimuPipe solver carries for a gas.
Worked example — 100 Nm³/h of air to standard, actual and mass flow
The converter's defaults: 100 m³/h of air entered at the Normal state (0 °C, 101.325 kPa — that is, 100 Nm³/h), with the Actual section set to a 7 bar(g) line at 20 °C and the Standard section on ISO 13443 (15 °C, 101.325 kPa).
- Mass: at 0 °C and 101.325 kPa air (M = 28.964 g/mol) has ρ = P·M/(R·T) = 1.2922 kg/m³, so 100 Nm³/h is 129.2 kg/h (both shown to the converter's display precision; the full-precision value carries through) — the mass-flow value from which every volumetric result is obtained.
- Normal: 100.0 Nm³/h — the input state is the normal state, so this is the identity.
- Standard (ISO 13443, 15 °C): the same mass at 288.15 K occupies 288.15/273.15 = 1.0549 times as much (5.49 % more), 105.5 Sm³/h; in cubic feet that is 62.1 SCFM on this basis — on the US 60 °F / 14.696 psia basis (288.706 K, 101.325 kPa) the temperature ratio alone makes it 0.19 % larger.
- Actual (20 °C, 7 bar(g) + 1.01325 = 8.013 bar(a)): ρ = 9.522 kg/m³, so the gas really occupies only 13.57 m³/h (7.99 ACFM) in the line — about 7.4 times smaller than its normal volume, which is what the pipe velocity and pressure drop see.
These figures are computed by the same function the converter runs; the defaults reproduce them. Switching the gas changes only the mass flow — the volume conversions are density ratios in which M cancels.
Assumptions and limits
- Ideal gas (Z = 1) throughout. Exact for the reference-state conversions by definition; for the Actual section at high line pressure the real volume is Z times the ideal one — under 0.5 % for air, nitrogen or methane below 10 bar, but several percent for CO₂ or propane at 20–50 bar. The SimuPipe solver applies Peng-Robinson Z for those gases.
- Dry gas. Compressor ratings per ISO 1217 / CAGI and ANR flows are for dry air; a humid intake carries 1–2 % water vapour by volume at 25 °C, which this converter neither adds nor removes — correct a wet-gas volume for its vapour content separately before or after converting.
- Absolute pressures. Gauge entries have 101.325 kPa added; at altitude the true atmospheric pressure is lower (about 1.2 % per 100 m near sea level on the standard atmosphere), which matters only for the Actual section and for gauge-referenced inputs.
- The Normal state is fixed by DIN 1343 (0 °C, 101.325 kPa). "Standard" has no single definition — the four offered are the common ones; a datasheet or contract may use yet another (US state bases run from 14.65 to 15.025 psia), and NTP (20 °C) is sometimes mislabelled as standard.
- Molecular masses are preset values for pure gases; the natural-gas figure is typical, and any mixture needs its analysed M. Mass flow scales directly with M, so a 5 % error in M is a 5 % error in kg/h.
- A conversion, not a measurement correction: orifice-meter, turbine or thermal-mass flow-meter readings referenced to a different state need the meter's own correction (AGA Report 3 / ISO 5167), which is more than the density ratio used here.
The same normal ↔ mass basis is what the SimuPipe solver uses for a gas Source flow, and its accuracy is documented case by case on the validation page.
References
Reference-state definitions and constants behind this page:
- DIN 1343:1990. Referenzzustand, Normzustand, Normvolumen — Begriffe und Werte — the normal state (Normzustand) 0 °C / 101.325 kPa that Nm³ refers to.
- ISO 13443:1996. Natural gas — Standard reference conditions — the 15 °C / 101.325 kPa standard reference conditions for natural gas.
- ISO 1217:2009. Displacement compressors — Acceptance tests; ISO 6358-1:2013. Pneumatic fluid power — Determination of flow-rate characteristics (ANR) — the 20 °C / 100 kPa dry-air basis of compressor ratings and pneumatic ANR flows.
- GPSA. Engineering Data Book, 14th ed., Section 1 (Conversion factors) and Section 23 (Physical properties) — US standard conditions (60 °F, 14.696 / 14.73 psia), conversion factors and gas properties.
- CODATA 2018 recommended values — R = 8.314 462 618 J/(mol·K), exact since the 2019 SI redefinition. physics.nist.gov — the universal gas constant used in the density relation.
Frequently Asked Questions
What is the difference between actual, normal, and standard flow?
Actual flow (ACFM, actual m³/h) is the volume the gas really occupies at line temperature and pressure. Normal flow (Nm³/h) re-expresses the same mass flow at 0 °C and 101.325 kPa (DIN 1343). Standard flow (Sm³/h, SCFM) does the same at a "standard" state, commonly 15 °C / 101.325 kPa (ISO 13443) or 60 °F / 14.696 psia in the US. The mass flow is identical in every case — only the reference volume changes. Compressed air example: 100 Nm³/h of air at 7 bar(g) and 20 °C occupies only about 13.6 m³/h of actual pipe volume.
How do I enter SCFM, ACFM, or Nm³/h in this converter?
Pick the plain scale under From unit and let the input conditions carry the reference state. For SCFM, choose ft³/min (CFM) and set the Standard preset to 60 °F / 14.696 psia (US gas industry). For Nm³/h, choose m³/h with the Normal (DIN 1343) preset — and for Sm³/h, the same with the ISO 13443 preset. For ACFM or any other actual flow, choose ft³/min (or m³/h) and type your line temperature and pressure into the input-conditions fields; the preset then shows Custom, which is correct — actual flow is referenced to your line state, not to a standard.
How do I convert SCFM to Nm³/h?
Multiply by the cubic-feet-to-cubic-metres factor (0.02832) and correct for the temperature difference between the two reference states. On the 60 °F US basis, 1 SCFM = 1.699 standard m³/h, and correcting 15.6 °C down to 0 °C gives about 1.61 Nm³/h. On a 68 °F (20 °C) basis the factor is about 1.58. The spread between those numbers is exactly why you should state the reference conditions rather than quote a bare conversion factor.
Why does "standard" mean different things in different industries?
The reference states grew up independently: the international natural gas industry settled on 15 °C / 101.325 kPa (ISO 13443), the US gas industry on 60 °F / 14.696 psia, compressor manufacturers on 20 °C / 100 kPa dry air (ISO 1217, used by CAGI), and laboratories on 20 °C or 25 °C variants. The differences are only a few percent, but on a compressor purchase or a billing meter a few percent matters. This converter makes the choice explicit instead of hiding it.
How do I convert Nm³/h to kg/h?
Multiply by the gas density at normal conditions: density = P·M / (R·T) with P = 101,325 Pa, T = 273.15 K, M the molecular mass. For air (M = 28.964 g/mol) that gives 1.292 kg/m³, so 100 Nm³/h of air is about 129 kg/h. For methane (M = 16.043 g/mol) it is 0.716 kg/m³, so 100 Nm³/h is about 72 kg/h.
Does this converter account for real-gas compressibility?
No — it uses the ideal gas law (Z = 1). That is accurate for converting between reference conditions, which are all near atmospheric, and for actual-flow conversion at modest line pressures. At high line pressures the actual volume deviates by the compressibility factor Z (a few percent for air at tens of bar, more for CO₂ or heavy hydrocarbons near their critical points). SimuPipe's pipe network simulator applies a Peng-Robinson equation of state for those cases.
Do SCFM ratings include humidity?
Some definitions do. ISO 1217 / CAGI compressor ratings reference dry air (0% relative humidity), while the older ASME "standard air" definition used 68 °F, 14.696 psia and 36% relative humidity. This converter assumes dry gas. The water-vapour correction is small at typical intake conditions but is worth checking when comparing compressor capacity claims.
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