Example:
15 nJ = 1.421726e-11 Btu (IT), Btu
1 nJ = 9.478171e-13 Btu (IT), Btu | 1 Btu (IT), Btu = 1.055056e+12 nJ
Conversion Steps:
15 × (1e-9 / 1055.05585262) = 1.421726e-11