Example:
15 Btu (IT), Btu = 9.877711e+19 keV
1 Btu (IT), Btu = 6.585141e+18 keV | 1 keV = 1.51857e-19 Btu (IT), Btu
Conversion Steps:
15 × (1055.05585262 / 1.602177e-16) = 9.877711e+19