The flammability range of natural gas is 5% to 15% by volume in air. This means that natural gas will only ignite and burn if the concentration of methane in the air is between 5% and 15%.

Here's what this means:

* Below 5%: The mixture is too lean to ignite.

* Between 5% and 15%: The mixture is within the flammable range and will ignite if an ignition source is present.

* Above 15%: The mixture is too rich to ignite.

It's important to note that this range can vary slightly depending on the composition of the natural gas and the temperature and pressure of the environment.