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Engineering ToolBox > Wobbe Index and Fuel Gases
The Wobbe Index is a number indicating the interchange ability of fuel gases. It is the best indicator of the similarity between a specific natural gas and propane-air mixture.
| Fuel Gas | Upper Wobbe Index (kcal/Nm3) | Lower Wobbe Index (kcal/Nm3) |
| Hydrogen | 11,528 | 9,714 |
| Methane | 12,735 | 11,452 |
| Ethane | 16,298 | 14,931 |
| Ethylene | 15,253 | 14,344 |
| Natural Gas | 12,837 | 11,597 |
| Propane | 19,376 | 17,814 |
| Propylene | 18,413 | 17,180 |
| n-Butane | 22,066 | 20,336 |
| Iso-Butane | 21,980 | 20,247 |
| Butylene-1 | 21,142 | 19,728 |
| LPG | 20,755 | 19,106 |
| Acetylene | 14,655 | 14,141 |
| Carbon Monoxide | 3,060 | 3,060 |
The Wobbe index relates fuel gas heating characteristics in a manner that is useful for blending fuel gases, or to obtain a constant heat flow from a gas of varying composition.
Note! The Wobbe Index does not relate flame temperature, heat transfer coefficients or temperature gradients.