The British thermal unit (Btu) is defined as the amount of energy required to raise the temperature of one pound (lb.) of water by one-degree Fahrenheit (°F) 5. 1 Btu 1 lb. x 1°F ie (cal) is defined as the amount of energy required to raise the temperature The calor of one gram (g) of water by one degree Celsius (°C): 1 cal-1 g x 10. energy, the Joule (I), is defined as the force of one Newton moving a di meter. 4.184 J turns out to be equivalent to 1 calorie. One pound contains 453.592 grams Use the factor cancel method to find out how many Joules in 1 Btu (approximately 1000 J).