Useful Tools / %LEL, %Vol & PPM Converter

%LEL, %Vol & PPM Converter

Convert flammable gas concentration between percent of the lower explosive limit (%LEL), percent by volume (% vol) and parts per million (ppm). LEL and UEL reference values stay visible with the results.

Choose gas and concentration

Reference limits are editable so you can match the gas and reference used by your own device or standard.

Gas selection

Lower explosive limit (LEL, % vol)

Upper explosive limit (UEL, % vol)

Input concentration

Input unit

Gas concentration result

Displayed flammability limits refer to the selected gas or manually entered values.

Selected LEL5 % vol

Selected UEL15 % vol

Percent of lower explosive limit—

Percent by volume—

Parts per million—

Reference concentration comparison

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Reference: NIOSH/OSHA

Safety: Below LEL and above UEL do NOT mean safe. Oxygen, pressure, temperature, dilution and gas mixtures change flammability. Toxic hazards can exist well below LEL. Never use this calculation to certify a safe atmosphere or bypass a gas detector.

How %LEL conversion works

% vol = (%LEL ÷ 100) × LEL (% vol); ppm = % vol × 10,000; %LEL = (% vol ÷ LEL) × 100. For methane with LEL 5% vol, 50%LEL corresponds to 2.5% vol or 25,000 ppm. The calculated %LEL value may exceed 100% and is not capped; a reading above UEL must not be interpreted as safe.

Gas data and reference limitations

Initial reference limits are taken from openly available CDC/NIOSH, CDC/ATSDR and ASHRAE data for individual substances. The selected limits are displayed and editable. Butane means n-butane, not a mixed LPG stream. Published LEL/UEL can differ across references, test conditions and mixture composition; current detector documentation and the applicable standard take precedence. The reference values generally concern gas or vapor in air near room conditions.

Reference pages: Methane (CDC/ATSDR) · Propane (NIOSH) · n-Butane (NIOSH) · Hydrogen (ASHRAE) · Carbon monoxide (NIOSH) · Hydrogen sulfide (NIOSH) · Ammonia (NIOSH) · Acetylene (NIOSH) · Ethanol vapor (NIOSH).

For custom gas, enter your own verified LEL and UEL; the calculator does not independently verify them. The custom input must have a positive LEL and a UEL greater than the LEL. Gas Concentration Converter calculates mass/volume concentration using gas molecular weight.