Factor to convert HBA1 to HBA1c 

I am sorry but I am trying to find the correct factor to change HBA1 to HBA1c, I would like to know if somebody can send this factor to me and also the explanation of the way to obtain that factor. 

I hope somebody can help me with that.

My name is Nancy and my e-mail address is:  nancychavezch@hotmail.com

Thank's 201.216.146.23