How do I convert ppm to % by volume?

100% means 100 parts out of 100:

  • 100% of anything means it is all the same thing

10%, means 10 parts out of 100, (1/10th of 100), so therefore its 90% something else.

  • 1% means 1 part out of a 100

Eventually we go down to 0.1%, 0.01%, 0.001%, but these numbers get kind of cumbersome, so it becomes convenient to change scale.

100% also means 1 million out of a million

Therefore, 10% is the same as 100,000 parts of a million (ppm).

1% is the same as 10,000 parts per million.

This one is important, 1% = 10,000 ppm.

 1% = 10,000 ppm

  • 0.1% = 1000 ppm
  • 0.01% = 100 ppm
  • 0.001% = 10 ppm
  • 0.0001% = 1 ppm = 1000 ppb
  • 0.000001% = 0.1 ppm = 100 ppb
  • 0.0000001% = 0.01ppm = 10 ppb
  • 0.00000001% = 0.001 ppm = 1 ppb = 1000 ppt (parts per trillion)

LEL (Lower Explosion Limit) to % to ppm examples: 

  • 100% LEL = 5% methane = 50,000 ppm methane
  • 10% LEL = 0.5% methane = 5000 ppm methane
  • 1% LEL = 0.05% methane = 500 ppm methane

Link to LEL Conversions

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1 Comments

  • Avatar
    Mike Dexter

    Should a customer send a request and only mentions the % LEL level then you must either quote both EU and Global standards.

    Example: 2.5% CH4 vs 2.2% CH4

    If unsure then please ask the customer to confirm the % VOLUME they require or refer them to the instrument manufacturer.

    Thanks

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