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mg/m³ to PPM (Air) Converter
↔ Convert ppm (air) to mg/m³ instead

Common Conversions

mg/m³ ppm (air)
0.1 2.445/MW
0.5 12.225/MW
1 24.45/MW
2 48.9/MW
5 122.25/MW
10 244.5/MW
25 611.25/MW
50 1222.5/MW
100 2445/MW
500 12225/MW
1000 24450/MW
10000 244500/MW

Why this conversion matters in chemistry

Common case: industrial-hygiene exposure assessment. A passive-sampler analytical result for toluene at 40 mg/m³ becomes 10.6 ppm against the OSHA PEL-TWA of 200 ppm. The conversion needs molecular weight because mg/m³ is mass per volume, while ppm in air is a volume or mole ratio. The 24.45 factor comes from the ideal-gas law at 25 °C, 1 atm — change the temperature and the molar volume changes too. The conversion sits at the handoff between analytical-side mass concentrations and the ppm values exposure limits use.

Formula

ppm = (mg/m³ × 24.45) ÷ MW

Worked Examples

1 mg/m³ (MW 28, CO) = 0.873 ppm

Carbon monoxide at 25 °C — useful as a low-MW reference.

1 mg/m³ (MW 46, NO₂) = 0.531 ppm

Nitrogen dioxide — about half the ppm value of CO at the same mg/m³.

10 mg/m³ (MW 78, benzene) = 3.134 ppm

Benzene vapor — the kind of figure an industrial-hygiene PEL check produces.

5 mg/m³ (MW 64, SO₂) = 1.910 ppm

Sulfur dioxide — a typical mid-range PEL exposure result.

Frequently Asked Questions

How do I convert mg/m³ to ppm in air?
Multiply by 24.45 and divide by molecular weight: ppm = (mg/m³ × 24.45) / MW. The 24.45 L/mol factor is the ideal-gas molar volume at 25 °C and 1 atm.
Why does this need molecular weight?
Because mg/m³ measures mass per volume while ppm in air is a mole or volume ratio. The molecular weight bridges mass and moles, which is what the gas-phase ppm definition needs.
Does temperature affect the conversion?
Yes. The 24.45 L/mol value is the molar volume at 25 °C and 1 atm. At other temperatures, recalculate molar volume from PV = nRT — at 0 °C and 1 atm it's 22.41 L/mol, the older STP reference.