I know that the full-width-half-maximum of the peak must be in radians, but when I measured the FWHM, it is in 2 theta. I found on the internet a formula wich tells me that "the Scherrer formula uses the FWHM of the peak in THETA and not in 2THETA". Do I need to half it to be in theta before insert it into the equation? This is important because doing so doubles the result you get for crystal size.