The general recommendation concerning sizes and menstrual cups is usually that if you are under 30 and have not given birth, you should choose the smaller size. And if you are over 30 and have given birth, then you should choose the larger menstrual cup. We at Flowcup know that women’s genitals are very individual, that we bleed different amounts and have varying degrees of genital sensitivity. Therefore, it is our recommendation that you choose a menstrual cup based primarily on how heavy your periods are. If you are unsure which size would suit you, then we recommend choosing the smaller size, as the menstrual cup holds almost four times as much menstrual fluid as a tampon.