ppm to mg/Nm³ Converter
Engineering Guide · Design Calculators
ppm is a volume fraction and mg/Nm³ is a mass per unit volume, so the two are converted using the gas's molecular weight and the molar volume of an ideal gas. Emission concentrations in mg/Nm³ are usually referenced to 0°C and 101.325 kPa (normal conditions); check the reference stated in the applicable permit.
| Gas | MW | 1 ppm = mg/Nm³ | 1 mg/Nm³ = ppm |
|---|---|---|---|
| NO | 30.006 | 1.339 | 0.747 |
| NO₂ | 46.006 | 2.053 | 0.487 |
| SO₂ | 64.064 | 2.858 | 0.350 |
| HCl | 36.461 | 1.627 | 0.615 |
| HF | 20.006 | 0.893 | 1.120 |
| NH₃ | 17.031 | 0.760 | 1.316 |
| CO | 28.010 | 1.250 | 0.800 |
| H₂S | 34.081 | 1.521 | 0.658 |
mg/Nm³ = ppm × M ÷ VmM molecular weight (g/mol), Vm molar volume of an ideal gas (L/mol): 22.414 at 0°C and 1 atmppm = mg/Nm³ × Vm ÷ MA different reference temperature gives a different result. The same 100 ppm of NO₂ is 205.3 mg/Nm³ at 0°C but 188.0 mg/m³ at 25°C. Check which reference the data you are comparing uses.
Most nitrogen oxides in flue gas leave the combustion zone as NO, but emission concentrations are often reported as NO₂. In that case use the NO₂ molecular weight (46.006). Converting with the NO molecular weight gives a mg/Nm³ value about 35% lower for the same ppm, so check the conversion method specified in your emission limit.
24.45 is a commonly quoted approximation of the molar volume of an ideal gas at 25°C and 1 atm; the exact value is 24.465 L/mol. When the reference is 0°C and 1 atm, as with normal cubic meters (Nm³), use 22.414.
No. This calculator only changes units. Moisture and oxygen correction are done separately in the oxygen correction calculator.
Both refer to gas volume at reference conditions, but the reference temperature differs between sources. Nm³ usually means 0°C and 1 atm, while “standard” conditions may be defined at 0°C, 15°C, 20°C or 25°C depending on the standard or regulation. Check the reference temperature stated in the data before comparing results.
By the Micro-one R&D Center · Last updated November 1, 2026 · All Engineering Guide pages →
Copyright © Micro-one Co., Ltd. All rights reserved.