ppm ↔ mg/m³ Converter
e.g. benzene = 78.11
1.00 ppm =
3.19 mg/m³
Using molar volume Vm = 24.45 L/mol at 25.00 °C
Reference only. Not legal or regulatory advice. Verify against the primary source before you act.
How it works
For gases and vapours, an airborne concentration in ppm (parts per million by volume) can be converted to a mass concentration in mg/m³ — but only if you know the substance's molecular weight and the temperature, because the volume a mole of gas occupies changes with temperature.
The conversion uses the molar gas volume:
- Vm = 24.45 × (T + 273.15) / 298.15L/mol (24.45 L/mol is the reference molar volume at 25 °C and 1 atm)
- mg/m³ = ppm × MW / Vm
- ppm = mg/m³ × Vm / MW
Reference conditions. The constant 24.45 L/mol is the molar gas volume at 25 °C and 1 atm(101.325 kPa, 760 torr) — the same basis OSHA states for the ppm values in Table Z-1. Changing the temperature rescales Vm; pressure is assumed to stay at 1 atm, so results are not adjusted for altitude or for a pressurised line.
This converts concentrations only — it does not include any exposure limits (no TLVs, PELs, or RELs). Look up a substance's federal OSHA PEL separately once you have converted units.
Worked example
Benzene (MW 78.11 g/mol) at 1 ppm at 25 °C and 1 atm: Vm = 24.45 L/mol, so 1 × 78.11 / 24.45 ≈ 3.19 mg/m³.
Related tools
Data vintage
- Data: ppm to mg/m³ conversion constant, U.S. National Institute for Occupational Safety and Health.The formula is stated for reference conditions of 25 °C and 1 atm, so a converted value belongs to those conditions and not to another temperature or pressure.
last updated 2026-08-07