Wobbe Index Calculator for gross or net heating value, gas relative density, reverse solves, energy-unit conversion, and two-gas comparison.

Choose a solve target, then complete the visible required fields marked with *.

Keep both gases on the same basis and reference conditions.

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Wobbe Index Formula

The following example problem outlines the steps and information needed to calculate the Wobbe Index.

WI = Vc / (Gs)1 / 2

Variables:

  • WI is the Wobbe Index (same units as Vc, e.g., Btu/ft³ or kJ/m³)
  • Vc is the HHV value for the fuel per unit volume (e.g., Btu/ft³) 
  • Gs is the specific gravity (relative density) of the fuel gas relative to air at the same reference conditions (dimensionless) 

To calculate a Wobbe Index, divide the HHV value for the fuel by the square root of the specific gravity of the fuel.

How to Calculate Wobbe Index?

The following steps outline how to calculate the Wobbe Index.

  1. First, determine the HHV value for the fuel (Btu/ft³). 
  2. Next, determine the specific gravity of the fuel (relative to air). 
  3. Next, gather the formula from above = WI = Vc / (Gs)^1/2.
  4. Finally, calculate the Wobbe Index.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

HHV value for the fuel (Btu/ft³) = 1050

specific gravity of the fuel = .61

WI = Vc / (Gs)^1/2 = ?