Example:
15 Btu (IT), Btu = 1.582584e+22 aJ
1 Btu (IT), Btu = 1.055056e+21 aJ | 1 aJ = 9.478171e-22 Btu (IT), Btu
Conversion Steps:
15 × (1055.05585262 / 1e-18) = 1.582584e+22