LEL stands for the lower explosive limit of a gas. It is the minimal concentration of the gas required for the gas to ignite. It is normally expressed as a percentage of the total air. PPM stands for parts per million. It also is a measure of concentration, though it is often provided by gas meters.

Multiply the LEL percentage number by 10,000 to get PPM.

To convert from PPM to an LEL percentage, divide the PPM by 10,000.

For example, ethylene has an LEL of 2.7 per cent. Multiplying this by 10,000 gives 27,000 PPM as the lower explosive limit, as it would be displayed on a gas meter.