About the atm to ppm Converter
This converter expresses a gas partial pressure in atmospheres as a concentration in parts per million by volume. It is useful for chemistry, environmental monitoring, gas mixing, and lab calculations where the total reference pressure is known.
How to use this calculator
- Enter the gas partial pressure in atm.
- Enter the total pressure in atm.
- Use 1 atm as the total pressure for the common direct atm-to-ppmv conversion.
- Read the concentration result in ppm.
- Check the additional ppmv, percent by volume, and mole fraction outputs.
How it works
The calculator uses the gas partial pressure and the total system pressure. Both inputs must be in atmospheres, with partial pressure non-negative and total pressure greater than zero.
Example calculation
If the gas partial pressure is 0.0004 atm and the total pressure is 1 atm, the pressure fraction is 0.0004 ÷ 1 = 0.0004. Multiplying by 1,000,000 gives 400 ppmv, which is also 0.04% by volume and a mole fraction of 0.0004.
Frequently asked questions
What is the formula to convert atm to ppmv?
ppmv = (partial pressure ÷ total pressure) × 1,000,000.
When should I use 1 atm as the total pressure?
Use 1 atm when the partial pressure is being compared to a standard total pressure of 1 atmosphere, such as a simple pressure fraction conversion.
Why can ppmv be calculated from partial pressure?
For an ideal gas mixture, the pressure fraction equals the mole fraction and volume fraction, so multiplying that fraction by 1,000,000 gives ppmv.
Can the result be greater than 1,000,000 ppm?
Yes, but that means the entered partial pressure is greater than the total pressure, which is usually a sign that the inputs or reference pressure should be checked.