The British Thermal Unit (BTU) is a traditional unit of energy commonly used in the United States, defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In the International System of Units (SI), energy is measured in joules, with one kilojoule (kJ) equaling 1,000 joules. To convert BTUs to kilojoules, multiply the number of BTUs by approximately 1.05506, since 1 BTU is equal to about 1.05506 kJ. For example, 5 BTUs is equivalent to 5.2753 kJ. Conversely, to convert kilojoules to BTUs, multiply the number of kilojoules by approximately 0.947817, as 1 kJ equals about 0.947817 BTU. These conversions are essential in fields like heating, ventilation, and air conditioning (HVAC), where both units are used to quantify energy.