Multiply the number of joules by 0.000947817 to convert to Btu. For example, if you have 19,000 J, multiply 19,000 by 0.000947817 to get 18.01 Btu.
Divide the number of joules by 1055.055986545 to convert to Btu. In this example, verify your answer by dividing 19,000 by 1055.055986545 to confirm your answer of 18.01 Btu.
Verify your answer with an online joules-to-Btu calculator. Enter the number of joules and the site will display the equivalent number of Btu.