Compressed Air Flow Unit Converter
Convert Nm³/hr, CFM, SCFM, l/min and kg/hr instantly — and settle the Normal vs Standard vs Actual confusion once and for all. Type into any box; everything else updates live.
These units all describe the same mass of air — they just reference it to different conditions. Type a value anywhere.
ACFM / actual m³/hr is the volume air really occupies at its own pressure and temperature. Inside a pressurised pipe that volume is far smaller than the free-air figure — this is where sizing mistakes happen.
A flow meter installed in the pipe reads actual volume unless it is a thermal mass or vortex type with built-in compensation. If your meter reads m³/hr without knowing line pressure, this is the correction you are missing.
Measuring flow for real?
WiseAir thermal mass flow sensors read directly in Nm³/hr with no pressure or temperature correction needed — so the number on the display is the number you can put in a report.
Normal vs Standard vs Actual — the difference that costs money
Normal (Nm³, Nl) references air to 0 °C and 1013.25 mbar. This is the European and Indian convention, and it is what almost every compressed air specification in India means when it says “m³/hr”.
Standard (Sm³, SCFM) references air to a warmer condition. Confusingly, “standard” is not one thing: ISO 1217 Annex C uses 20 °C / 1000 mbar for compressor FAD ratings, the common European Sm³ uses 20 °C / 1013.25 mbar, and US SCFM uses 60 °F / 14.696 psia. A Nm³ contains about 7% more air than a 20 °C Sm³ — enough to fail an acceptance test.
Actual (ACFM, m³/hr actual) is the real volume at whatever pressure and temperature the air happens to be. At 7 bar(g), one normal cubic metre squeezes into roughly one-eighth of a cubic metre. Size a pipe on ACFM when you meant Nm³/hr and you will undersize it badly.
The practical rule: when anyone quotes you a flow, ask which of the three they mean, and at what reference conditions. If the answer is vague, the number is not usable.
Conversion factors — quick reference
| From | To | Multiply by |
|---|---|---|
| Nm³/hr | CFM (0 °C basis) | 0.5886 |
| Nm³/hr | SCFM (60 °F) | 0.6221 |
| Nm³/hr | Sm³/hr (20 °C) | 1.0732 |
| Nm³/hr | Nl/min | 16.667 |
| Nm³/hr | kg/hr (dry air) | 1.2923 |
| CFM (0 °C basis) | Nm³/hr | 1.6990 |
| SCFM (60 °F) | Nm³/hr | 1.6075 |
| Actual m³/hr | Nm³/hr | (Pabs/1.01325) × (273.15/TK) |
Frequently asked questions
How do I convert Nm³/hr to CFM?
Multiply by 0.5886 if both are on the normal 0 °C basis, or by 0.6221 if the CFM figure is US SCFM at 60 °F. Most Indian compressor datasheets quoting “CFM” actually mean free air delivery at ambient, which sits between the two — within about 5%, which is usually inside the measurement uncertainty anyway.
My compressor is rated 500 CFM. What is that in Nm³/hr?
About 850 Nm³/hr on a normal basis. Check whether the rating is FAD per ISO 1217 Annex C — if so it is referenced to 20 °C and 1000 mbar at the inlet, and you should confirm the actual site inlet conditions before treating it as guaranteed.
Why does my flow meter read lower than the compressor rating?
Usually one of three things: the meter reads actual volume rather than normal, the compressor is not delivering rated FAD (worn element, blocked filters, high inlet temperature), or the meter is installed too close to a bend and is seeing a distorted profile. Thermal mass meters need roughly 15 pipe diameters of straight run upstream.
Is Nm³ the same as Sm³?
No. A normal cubic metre at 0 °C holds about 7% more air molecules than a standard cubic metre at 20 °C. On a 1,000 m³/hr system that is a 70 m³/hr disagreement — big enough to swing an energy calculation or a contractual guarantee.
What is the difference between ACFM and SCFM?
ACFM is the actual volume the air occupies at its own pressure and temperature. SCFM references the same mass of air to a fixed standard condition. At 7 bar(g), one normal cubic metre occupies roughly one eighth of a cubic metre of actual volume.
Dry air properties used: molar mass 28.9647 g/mol, normal density 1.2923 kg/m³ at 0 °C / 1013.25 mbar. Ideal gas behaviour is assumed, which is accurate to well within 1% across normal compressed air pressures. Related tools: Leak Cost Calculator · Pressure Dew Point Calculator.
