Wobbe index

The Wobbe index of a gas is a measure of the energy that will flow through a given burner orifice. If V_C is the higher heating value, or higher calorific value, and G_S is the specific gravity, the Wobbe index, I_W, is defined as:

$I_{W}={\frac {V_{C}}{\sqrt {G_{S}}}}.$

(1)

While it is referred to as an index or number, the Wobbe index has the same units as the heating value.