PPM (Air) to mg/m³ Converter
Common Conversions
| ppm (air) | mg/m³ |
|---|---|
| 0.1 | MW/244.5 |
| 0.5 | MW/48.9 |
| 1 | MW/24.45 |
| 2 | MW/12.225 |
| 5 | MW/4.89 |
| 10 | MW/2.445 |
| 25 | MW/0.978 |
| 50 | MW×2.044 |
| 100 | MW×4.089 |
| 500 | MW×20.45 |
| 1000 | MW×40.90 |
| 10000 | MW×409.0 |
Why this conversion matters in chemistry
Industrial-hygiene compliance is the usual setting. The OSHA PEL-TWA for carbon monoxide at 50 ppm becomes 57.2 mg/m³ on a personal breathing-zone analytical result for a stationary-source emissions audit (CO at MW 28). The conversion uses ideal-gas molar volume (24.45 L/mol at 25 °C, 1 atm). In practice, this is the unit handoff between OSHA mole-ratio limits and the mass-concentration form analytical methods report results in.
Formula
mg/m³ = (ppm × MW) ÷ 24.45
Worked Examples
1 ppm CO (MW 28) = 1.145 mg/m³
Carbon monoxide at OSHA-relevant low ppm levels.
1 ppm NO₂ (MW 46) = 1.882 mg/m³
Nitrogen dioxide — about a typical urban-air monitoring level.
5 ppm benzene (MW 78) = 15.95 mg/m³
Benzene vapor — about the kind of figure a PEL exposure check produces.
10 ppm SO₂ (MW 64) = 26.18 mg/m³
Sulfur dioxide — about a moderate industrial-exposure level.
Frequently Asked Questions
How do I convert ppm to mg/m³ in air?
Multiply by molecular weight and divide by 24.45 L/mol: mg/m³ = (ppm × MW) / 24.45. The 24.45 factor is the ideal-gas molar volume at 25 °C and 1 atm.
What is the 24.45 factor?
The molar volume of an ideal gas at 25 °C and 1 atm — 24.45 L/mol. At 0 °C and 1 atm (old STP), use 22.414 L/mol instead. The factor is reference-state dependent.
Where is this conversion used?
OSHA workplace exposure limits (PEL) report in ppm; WHO guidelines and many international air-quality limits report in mg/m³. Bridging the two units is the routine first step in industrial-hygiene compliance work.