A British thermal unit, or Btu, is a common measurement of energy and is often used to express the amount of energy contained in a quantity of natural gas. Natural gas is generally measured in one of two ways - by volume or by energy content. Volumetric units typically used are cubic foot (cf) or cubic meter (m3). But because the energy content (or heating value) of natural gas in a given volume can vary, a more accurate way of measuring the ultimate value of gas is to use units based on energy content.
The most commonly used unit to measure energy content in natural gas is the Btu, which is equal to the amount of energy required to raise the temperature of 1 pound of water 1 degree Fahrenheit at sea level. Because a Btu is a relatively small amount of energy, more commonly used are units expressing multiples of Btus including therms which are equal to 100,000 Btus, or decatherms (Dth) or millions of Btus (MMBtu) which are both equal to 1,000,000 Btus.