LNG units can be complex because different units are used to measure natural gas in its gaseous and liquid forms. And since LNG is a global business, both metric and English units are used.
LNG is typically measured in volumetric units. When in liquid form, LNG is commonly measured in metric tonnes. But you will sometimes see it measured in the amount of gas that it will provide when converted back to gaseous form. In this case, common units are billions of cubic meters (bcm) or billions of cubic feet (Bcf). Annual capacities of flow rates of facilities are often described in million tonnes per annum or millions of tonnes per year (these are the same thing). Various abbreviations are used including MMtpa, mtpa, MMty/y, or million mt/yr. Tanker capacities are sometimes stated in cubic meters, but this can be confusing because this is cubic meters of liquid not gas.
Converting volumetric units to energy content is complicated by the fact that different cargos of LNG have different heating values depending on how it was processed and the requirements of the country to which it is being delivered. Heating values in Asia tend to be higher than in other countries due to local specifications.
Here are various conversions:
1 million tonnes (LNG) = 48.7 Bcf* (gas) = 1.379 bcm (gas)
1 Bcf (gas) = 45,000 cubic meters (LNG)
1 million tonnes per year (mtpa) (LNG) = 48.7 Bcf/year* (gas) = 1.379 bcm/year (gas)
1 cubic meter (m3) = 35.315 Cubic feet (cf)
1 tonne (LNG) = 53.57 MMBtu**
1 kilocalorie (kcal) = 4.187 kilojoule (kJ) = 3.968 Btu
1 Dth = 1 MMBtu = 10 therms = 1,000,000 Btu
* Assumes a specific gravity of LNG at .45
** Assumes a natural gas heating value of 1,100 Btu/cf