%LEL, %Vol & PPM Converter
Convert a flammable-gas concentration between %LEL, percent by volume and ppm using a gas-specific lower explosive limit. The selected LEL and UEL stay visible throughout the calculation.
Enter the gas and concentration
Choose a preset or enter an LEL/UEL pair from the SDS or instrument documentation.
Converted result
All three units use the same gas-specific LEL basis.
The calculated concentration is below 100% LEL for the selected reference. This does not by itself establish that the atmosphere is safe.
Understand the calculation before applying it
Select the correct gas
100% LEL represents the selected gas's lower flammability limit, not a universal concentration.
Confirm the reference
LEL and UEL values may vary with the source, test conditions, temperature, pressure and mixture composition.
Separate conversion from detection
This tool converts concentration units. Instrument response, calibration gas and correction factors must be evaluated separately.
%vol = (%LEL ÷ 100) × LEL%LEL = (%vol ÷ LEL) × 100ppm = %vol × 10,000LEL and UEL values used by this calculator
These presets are provided for convenient preliminary conversion. Confirm the value used by the actual instrument, SDS or governing standard.
| Gas or vapor | Formula | LEL (%vol) | UEL (%vol) | Primary reference |
|---|---|---|---|---|
| Methane | CH₄ | 5.0 | 15.0 | CDC/NIOSH |
| Propane | C₃H₈ | 2.1 | 9.5 | NIOSH Pocket Guide |
| Hydrogen | H₂ | 4.0 | 75.0 | NIOSH Pocket Guide |
| Carbon monoxide | CO | 12.5 | 74.0 | NIOSH Pocket Guide |
| Ammonia | NH₃ | 15.0 | 28.0 | NIOSH Pocket Guide |
| n-Butane | C₄H₁₀ | 1.6 | 8.4 | NIOSH Pocket Guide |
| Ethanol vapor | C₂H₅OH | 3.3 | 19.0 | NIOSH Pocket Guide |
| Acetylene | C₂H₂ | 2.5 | 100.0 | NIOSH Pocket Guide |
| Hydrogen sulfide | H₂S | 4.0 | 44.0 | NIOSH Pocket Guide |
| Ethylene | C₂H₄ | 2.7 | 36.0 | NIOSH Pocket Guide |
Continue your gas calculation
%LEL Converter FAQ
Is 10% LEL the same as 10% gas by volume?
No. For methane with a 5%vol LEL, 10% LEL equals 0.5%vol or 5,000 ppm. The equivalent concentration changes when a different gas and LEL are selected.
Why does the calculator need a specific gas?
Every gas or vapor has its own lower flammability limit. A %LEL reading is meaningful only when its gas and reference LEL are known.
Does a value below 100% LEL mean the atmosphere is safe?
No. Toxicity, oxygen level, local accumulation, detector uncertainty, alarm policy and applicable regulations must also be considered. Many systems alarm well below 100% LEL.
Is a concentration above the UEL safe?
No. A mixture above the UEL can enter the flammable range when air is introduced or the gas disperses. It may also create toxicity or oxygen-displacement hazards.
Can this tool calculate a detector correction factor?
No. Correction factors depend on sensor technology, calibration gas, target gas, instrument design and manufacturer data. This page only converts concentration units using LEL and UEL references.