PPM to mg/m³ Calculator

ppm
g/mol
°C
mg/m³
Enter values above
Common Gases:
Calculation Steps:
mg/m³ = PPM × (MW ÷ Molar Volume)
Enter values above to see the step-by-step calculation breakdown.

PPM to mg/m³ Conversion Reference Table (at 25°C, 1 atm)

This table shows representative PPM to mg/m³ conversions for common gases at standard conditions. Use the calculator above for precise conversions at any temperature.

PPM Value Gas (MW g/mol) mg/m³ at 25°C
0.1 28.01 (CO) 0.115
0.5 46.01 (NO₂) 0.941
1 64.07 (SO₂) 2.620
5 48.00 (O₃) 9.816
10 78.11 (C₆H₆) 31.95
25 30.03 (CH₂O) 30.71
50 17.03 (NH₃) 34.83
100 34.08 (H₂S) 139.4
200 28.01 (CO) 229.1
420 44.01 (CO₂) 756.0
1000 2.016 (H₂) 82.45
5000 28.01 (CO) 5,729

How to Use the PPM to mg/m³ Converter

The PPM to mg/m³ converter transforms gas-phase volumetric concentrations (parts per million) into mass-per-volume concentrations (milligrams per cubic meter). This conversion is essential for occupational health assessments, air quality monitoring, and regulatory compliance reporting.

Follow these steps to convert PPM to mg/m³:

  1. Enter the PPM concentration — type the volumetric gas concentration you want to convert.
  2. Enter the molecular weight — input the molecular weight (molar mass) of the specific gas or vapor in g/mol. Use a preset button for common gases like CO, NO₂, or ozone.
  3. Set the temperature — the default is 25°C (standard OSHA/NIOSH conditions). Adjust this if your measurement was taken at a different ambient temperature.
  4. Read the result — the mg/m³ value appears instantly, along with a step-by-step breakdown of the formula and arithmetic.

You can click any preset gas button to automatically fill in the molecular weight and a typical exposure concentration. The result updates in real time as you type, and you can copy it to your clipboard with one click.

How the PPM to mg/m³ Conversion Works

PPM (parts per million) is a dimensionless volumetric ratio: the number of gas molecules per million molecules of air. To express that same concentration as a mass per unit volume (mg/m³), you need the gas's molecular weight and the molar volume of air at the given temperature and pressure.

mg/m³ = PPM × (MW ÷ 24.45)

Where MW is the molecular weight in g/mol and 24.45 L/mol is the molar volume at 25°C and 1 atm.

The molar volume constant of 24.45 applies specifically at 25°C (298.15 K) and 1 atmosphere of pressure. At other temperatures, the molar volume is adjusted using the ideal gas law:

Molar Volume = 24.45 × ((T + 273.15) ÷ 298.15)

Where T is the ambient temperature in degrees Celsius.

Why molecular weight matters: Heavier gas molecules pack more mass into the same volume. A single PPM of sulfur dioxide (MW = 64.07) contains roughly 2.3× more mass per cubic meter than a single PPM of carbon monoxide (MW = 28.01). This is why the molecular weight of the target gas is a required input.

Accuracy considerations: The formula assumes ideal gas behavior, which is highly accurate for typical atmospheric concentrations at ambient temperatures and pressures. For very high pressures, extreme temperatures, or near-condensation conditions, real-gas corrections (such as the van der Waals equation) may be necessary.

PPM to mg/m³ FAQs and Common Questions

The formula is: mg/m³ = PPM × (Molecular Weight ÷ 24.45) at 25°C and 1 atm. The constant 24.45 represents the molar volume of an ideal gas at standard conditions (25°C, 1 atm). At different temperatures, the molar volume changes, so the conversion factor adjusts accordingly.
Temperature affects gas volume. As temperature increases, gas expands, lowering the mass per unit volume. The molar volume at temperature T (°C) is calculated as 24.45 × ((T + 273.15) / 298.15). This means the same PPM concentration represents fewer mg/m³ at higher temperatures and more mg/m³ at lower temperatures.
Common molecular weights: Carbon Monoxide (CO) = 28.01 g/mol, Nitrogen Dioxide (NO₂) = 46.01 g/mol, Sulfur Dioxide (SO₂) = 64.07 g/mol, Ozone (O₃) = 48.00 g/mol, Benzene (C₆H₆) = 78.11 g/mol, Formaldehyde (CH₂O) = 30.03 g/mol, Ammonia (NH₃) = 17.03 g/mol, Hydrogen Sulfide (H₂S) = 34.08 g/mol.
No. PPM to mg/m³ conversion using the molecular weight and molar volume formula applies only to gases and vapors. For dissolved substances in liquids, 1 PPM equals approximately 1 mg/L (not mg/m³) in dilute aqueous solutions, because the density of water is approximately 1 kg/L.
OSHA and most industrial hygiene standards use 25°C (77°F) and 1 atmosphere (101.325 kPa), giving a molar volume of 24.45 L/mol. The NIOSH standard also uses 25°C. Some European standards and IUPAC use 0°C (273.15 K) and 1 atm, where the molar volume is 22.414 L/mol. Always confirm which reference conditions apply to your regulatory context.