Most menstrual cup brands offer at least two sizes, and picking the right one makes a real difference in comfort and leak protection. Unlike clothing sizes, cup sizing is based on a few specific physical factors rather than body size overall.
What Determines Cup Size
The two biggest factors are whether you've given birth vaginally, and how strong your pelvic floor muscles are, both affect how much your cervix sits and how much support the cup needs to stay in place and form a seal.
Age and Childbirth History
As a general starting point, brands typically recommend a smaller size for those under 30 who haven't given birth vaginally, and a larger size for those who have given birth vaginally or are over 30, since pelvic floor muscles can loosen somewhat with age or delivery. These are starting guidelines rather than strict rules.
Your Flow
A heavier flow generally benefits from a larger capacity cup so you don't need to empty it as often, while a lighter flow can often be managed comfortably with a smaller size. If you're between sizes, capacity is often the deciding factor.
Firmness Matters Too
Softer cups tend to be more comfortable for sensitive bladders but can be slightly harder to pop open, while firmer cups create a more reliable seal but may take more getting used to. If you have a strong pelvic floor or higher cervix, a firmer cup often works well; a softer cup can be gentler for beginners or those with a lower cervix.
If You're Still Unsure
When in doubt, many people find success starting with a smaller or medium size and a beginner-friendly firmness, then adjusting on their next purchase based on their experience. If you're brand new to cups altogether, pairing this with our beginner's guide to using a menstrual cup will help you get a full picture before you buy.