Measure your wrist in centimeters, and then add one centimeter, and that is the typical size that you should wear for your Cartier love bracelet. My wrist measures 16cm (6 1/4"), so I wear a 17.
I have a 17 in both the WG bangle and RG cuff. My SA initially told me to get a 16 but I was afraid that the sample one was hitting on a bone too much. So I have the 17s and I'm very happy with that size.
I'm glad you asked about this surfergirljen, I was wondering the same thing. My SA said I would be a size 17. I don't want mine to be too loose on my wrist.