Green Rays Cup comes in 3 sizes, aiming to fit you perfectly and to offer guaranteed Leak-Free Protection.
While the age and the number of births are a good indicator of which cup is right for you, there are users who successfully wear the "wrong" size and experience great comfort and no leakages.
The position of the cervix is individual to everyone and there are several heights which can all be considered "normal".
Additionally, for some of us, the position of the cervix is fluctuating during menstruation. If the cervix is sitting too low, then a long menstrual cup can feel uncomfortable. You can find out the height of your cervix by measuring it yourself: insert a clean finger in your vagina - if you feel the cervix at the first bend of your finger, then you have a low cervix and the Green Rays Cup Mini would be your best choice.
At the other extreme, if you do not reach your cervix, then it means that it is positioned high, and you will benefit from a longer period cup.
The menstrual flow can be a factor in choosing a suitable menstrual cup for you. If you have a heavy flow, then Size B might be more suitable for you since its capacity is of 40ml. That's averaging about 8 tampons if you consider that a medium tampon holds about 5 ml of menstrual blood.
Your individual vaginal condition and the strength of your pelvic floor might also have a say in the choice of your most suitable menstrual cup. Active users and those who know they have strong pelvic muscles might benefit more from a smaller cup. Give the Green Rays Cup Size A a go if you haven't gone through childbirth and you are very physically active knowing to have a strong vaginal muscles.
And here is a handy guide that will lead you to your cup.