Example preset
Select a preset to fill the inputs and show a reference result immediately.
Inputs
Results
Formula details appear after calculation.
What this tool converts
Convert gas ppm or ppb (volume mixing ratio) to mg/m³ (mass concentration), or convert mg/m³ back to ppm or ppb. The calculation uses the gas molecular weight, temperature, and pressure.
Why temperature, pressure, and molecular weight are required
ppm and ppb describe a proportion of gas, while mg/m³ describes mass in a volume. At the same ppm value, mg/m³ changes when the gas molecular weight, temperature, or pressure changes.
Formula and units
The ideal gas equation PV=nRT converts ppm or ppb to mole fraction, then molar concentration, and finally mass concentration. The calculator converts P to Pa, T to K, and uses MW in g/mol.
Formula (ppm→mg/m³): C = ppm × P × MW / (R × T) × 10^-3. For ppb, the final factor is 10^-6. Reverse modes solve the same relationship for ppm or ppb.
Standard-state presets
The 0°C, 20°C, and 25°C at 1 atm presets are shortcuts for entering temperature and pressure. They do not establish one universal standard state for every field or reporting method.
Gas presets and custom molecular weight
A gas preset fills in the molecular weight for the selected gas. If your gas is not listed, verify the molecular weight appropriate to your use and enter it in the custom field.
Limits of the ideal-gas approximation
Humidity and non-ideality corrections are not included. Moist gas, high pressure, low temperature, or strict reporting conditions may require additional corrections or a prescribed calculation method.
What this tool does not determine
This page only converts units. It does not determine AQI, health effects, exposure limits, environmental or emission limits, or regulatory compliance.
Frequently asked questions
What is the difference between ppm or ppb and mg/m³?
ppm and ppb are gas volume mixing ratios, which behave like mole fractions under the ideal-gas model. mg/m³ is mass per volume. They represent different quantities and cannot be exchanged without the gas conditions.
Why are molecular weight, temperature, and pressure needed to convert ppm to mg/m³?
Molecular weight relates the amount of gas to its mass, while temperature and pressure determine how much gas is present in a given volume. Changing any of these inputs changes the converted mass concentration.
Which standard state should I use, and what do the presets mean?
Use the temperature and pressure required by your application or reporting method. The 0°C, 20°C, and 25°C at 1 atm presets are input shortcuts, not a universal definition of standard state.
Can I use this for moist or non-ideal gases?
You can use it as an ideal-gas estimate, but it does not correct for humidity or compressibility. Check an appropriate correction or prescribed method when moisture, high pressure, low temperature, or non-ideality matters.
Is this the same as converting liquid ppm, mg/L, or mg/kg?
No. This page assumes a gas volume mixing ratio. Liquid ppm, mg/L, and mg/kg use different mass, volume, and density assumptions.
Can this determine AQI or compliance with health, exposure, environmental, or emission limits?
No. This calculator only converts units. It does not compare results with limits or make health, safety, environmental, or regulatory decisions.
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