Energy: natural gas: cubic metres to Joules

Self-tutoring about energy: the tutor mentions a conversion.

The following is according to my understanding.

I was reading about natural gas reserves of some countries, which are typically reported in cubic metres. Yet, importation and consumption figures seem to be reported sometimes in Joules. How does one connect them?

Apparently, a gigaJoule, or 1.0×10^9 J, is about 25.5 cubic metres of natural gas at standard conditions. It would seem, therefore, that one cubic metre of natural gas is around 3.9×10^7 Joules.

Source:

fortisbc.com