As I replied to your other post calcIrms sampling rate slower than expected - #5 by apurva_rana, you can find the theory about the calculations in the ‘Learn’ section of this website. All the calculations are done for you in the emonLib library.
If you are not getting the proper information out, then you are not putting the proper information in. I can assure you that the calculations in the library are correct for an Atmel ATMega 328P. If you are using a different processor, you might need to change one or more things.