The difference between 1 Mcf and 1 Mmcf of natural gas is 999,000 cubic feet. One Mcf equals 1,000 cubic feet, and 1 Mmcf equals 1,000,000 cubic feet; 1,000 is subtracted from 1,000,000 to determine the difference.
The amount of natural gas present is measured in cubic feet. An average home's basic natural gas needs for four days will use approximately 1,000 cubic feet of gas. This is typically converted into British thermal units, or BTU, or therms on a home's gas bill, which measures the heat potential generated from the gas. For example, a home that uses 100 cubic feet has used approximately 100,000 BTU, which is equal to 1 therm of natural gas.