The Wobbe Index (WI) represents the interchangeability of fuel gases such as natural gas, LNG. The value of Wobbe index is equal to BTU per cubic foot divided by the square root of the specific gravity. In almost all gas appliances, the flow of gas is regulated by making it pass through a hole or orifice. The usefulness of the Wobbe index is that for any given orifice, all gas mixtures that have the same Wobbe index will deliver the same amount of heat.
The higher gases Wobbe index indicates the greater the heating value of the quantity of gas that will flow through a hole of a given size in a given amount of time.
The wobbe index is important and should be defined in the specifications of gas supply and transport utilities because equipment is rated to operate over a specified Wobbe Index range.