Example:
15 Btu (th) = 9.871103e+19 keV
1 Btu (th) = 6.580735e+18 keV | 1 keV = 1.519587e-19 Btu (th)
Conversion Steps:
15 × (1054.349999974 / 1.602177e-16) = 9.871103e+19