From NIST sources.  This is a list of conversion factors to convert Units of Energy.  The factors in this table convert the Units to a system reference Unit of Joule.  

The conversions can be used to convert from or to any of the Units defined.  For example,  to convert from erg to joule, you would Multiply by the factor in this Table.  To convert from joule to watt hour (or other) use the factor in the Table as a divisor.

Notes

This data was gathered from the NIST appendix B document for units.  

This table of Energy conversion is standardized to contain the Factor to convert Units to joule.  

All units can be converted between other compatible units by converting the Units first to joule and then again to the desired Unit result.  For example to convert erg to Watt hour,  first use the conversion from erg to joule, and then apply the conversion from joule to Watt hour.