Example:
15 calorie (nutritional) = 59.564661 Btu (th)
1 calorie (nutritional) = 3.970977 Btu (th) | 1 Btu (th) = 0.251827 calorie (nutritional)
Conversion Steps:
15 × (4186.8 / 1054.349999974) = 59.564660693