Watts to BTU (IT) per second conversion calculator shown above calculates how many BTU (IT) per second are in 'X' watts (where 'X' is the number of watts to convert to BTU (IT) per second). In order to convert a value from watts to BTU (IT) per second (from W to BTU/s) just type the number of W to be converted to BTU/s and then click on the 'convert' button.