Here is a converter:
http://www.translatorscafe.com/cafe/units-converter/energy/calculator/-Btu%5D-to--kcal%5D/
1 BTU = 1,055 Joules
1 BTU(ISO) = 1,054.5 Joules 1 Joule = 0.00094832 BTU(ISO) (rounded)
MBH does not convert directly to BTU. MBH is 1,000 BTU/hr.
You cannot do so directly. They measure completely different things.