Is methane gas heavier than air?

It's not, methane weighs less than air. A mole of methane (CH4) weighs: 12 * 1 + 1 * 4 ~ 16 g. while a mole of air (78 % N2 + 21 % O2 + 1% Ar) weighs: 14 * 2 * 0.78 + 16 * 2 * 0.21 + 40 * 1 * 0.01 ~ 29 g. So methane is almost twice as light as air. read more

While leaks from a refrigerated liquid container are initially heavier than air due to the increased density of the cold gas, the gas at ambient temperature is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is the principal component. read more

Methane's (CH4) formula mass is 12+ 4 or just 16 - so it is lighter than air as the formula mass (and hence density) is less than 28. Carbon Dioxide (CO2) has a formula mass of 44 (12 + 16 + 16) so it is much more dense than air. read more