Milliwatts to calories per day conversion calculator shown above calculates how many calories per day are in 'X' milliwatts (where 'X' is the number of milliwatts to convert to calories per day). In order to convert a value from milliwatts to calories per day (from mW to cal/d) type the number of mW to be converted to cal/d and then click on the 'convert' button.