Gas Concentration Converter (ppm ↔ mg/m³)
Convert gas concentrations between ppm/ppb and mg/m³ or µg/m³ using the gas's molar mass, temperature and pressure.
Mass concentration
28.622 mg/m³
- ppm
- 25
- ppb
- 25,000
- mg/m³
- 28.622
- µg/m³
- 28,622
- Molar mass
- 28.01 g/mol
- Molar volume
- 24.465 L/mol
Assumes carbon monoxide behaves as an ideal gas in air at 25 °C and 101.325 kPa (molar volume 24.465 L/mol); ppm and ppb are by volume.
Show the work
Molar mass of CO
M = Σ atoms × atomic weight
12.011 + 15.999 = 28.01 g/mol
Molar volume of an ideal gas
Vm = R × T ÷ P
8.314462618 × (25 + 273.15) ÷ 101.325 = 24.465 L/mol
Mass concentration
mg/m³ = ppm × M ÷ Vm
25 × 28.01 ÷ 24.465 = 28.622 mg/m³
How it works
mg/m³ = ppm × M ÷ Vm, with molar volume Vm = R·T ÷ P (ideal gas, R = 8.314462618 J/(mol·K), exact). ppb is 1/1000 ppm; µg/m³ is 1000 × mg/m³.
ppm and ppb here mean parts per million/billion by volume (mole fraction) in air. The result depends on the temperature and pressure you enter — 25 °C and 101.325 kPa is the occupational-hygiene convention (Vm ≈ 24.47 L/mol); 0 °C gives 22.41 L/mol. Molar masses from the CIAAW 2024 standard atomic weights.
Questions
- How does the gas concentration converter work?
- mg/m³ = ppm × M ÷ Vm, with molar volume Vm = R·T ÷ P (ideal gas, R = 8.314462618 J/(mol·K), exact). ppb is 1/1000 ppm; µg/m³ is 1000 × mg/m³.
- What does it assume?
- ppm and ppb here mean parts per million/billion by volume (mole fraction) in air. The result depends on the temperature and pressure you enter — 25 °C and 101.325 kPa is the occupational-hygiene convention (Vm ≈ 24.47 L/mol); 0 °C gives 22.41 L/mol. Molar masses from the CIAAW 2024 standard atomic weights.
- Why do I need temperature and pressure?
- ppm counts molecules per million; mg/m³ is mass per volume. The same gas takes more volume when warm or at low pressure, so the mg/m³ figure changes with conditions.
- Does it match NIOSH's conversion factors?
- Yes at 25 °C and 1 atm: carbon monoxide 1 ppm ≈ 1.145 mg/m³ (NIOSH lists 1.15) and benzene 1 ppm ≈ 3.19 mg/m³.
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