Here are some frequently used units for measuring natural gas:

1 cubic foot (cf) = 1,027 Btu
100 cubic feet (1 ccf) = 1 therm (approximate)
1,000 cubic feet (1 Mcf) = 1,027,000 Btu (1 MMBtu)
1,000 cubic feet (1 Mcf) = 1 dekatherm (10 Therms)

100,000 Btu = 1 Therm
1 million (1,000,000) Btu = 1 Dekatherm