PPM to mg/m³ Gas Calculator
Gas exposure limits come in both PPM and mg/m³, and converting needs the molecular weight — unlike liquids, there is no universal 1:1. At 25°C and 1 atm, mg/m³ = PPM × MW ÷ 24.45.
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PPM to mg/m³ Gas Calculator
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Gas exposure limits come in both PPM and mg/m³, and converting needs the molecular weight — unlike liquids, there is no universal 1:1. At 25°C and 1 atm, mg/m³ = PPM × MW ÷ 24.45.
How to use this calculator
- Enter PPM.
- Enter molecular weight.
- Get mg/m³ (25°C, 1 atm).
- Adjust if conditions differ.
The formula
24.45 L is the molar volume of an ideal gas at 25°C/1 atm.
What the units mean
PPM (parts per million) — one part of solute per million parts of the total mixture. The workhorse unit for trace concentrations in water, air, and food.
Assumption: Gas conversions depend on temperature and pressure. This uses 25 °C and 1 atm (molar volume 24.45 L/mol); correct the molar volume if your conditions differ.
Worked example
50 PPM CO (MW 28.01): 50 × 28.01 ÷ 24.45 ≈ 57.3 mg/m³.
Quick reference
| Gas | 50 PPM in mg/m³ |
|---|---|
| CO (28.01) | 57.3 |
| CO₂ (44.01) | 90.0 |
| NH₃ (17.03) | 34.8 |
At 25°C, 1 atm.
Where you will actually use this
OSHA PELs and ACGIH TLVs are published in both units; you need to move between them.
- Exposure limit compliance
- Air monitoring
- Industrial hygiene
Mistakes that give wrong answers
- Forgetting temperature/pressure corrections
- Using liquid-phase 1:1 assumption for gases
Key takeaways
- Formula: mg/m³ = PPM × MW ÷ 24.45 [25°C, 1 atm]
- Remember: At 25°C, 1 atm.
- Watch out for: Forgetting temperature/pressure corrections
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
What is 24.45 in the formula?
The molar volume (L/mol) of an ideal gas at 25°C and 1 atm.
Does temperature change the conversion?
Yes — molar volume changes with T and P.