Most people can comfortably use both sizes, but one may be a better fit than the other. Some things that you might want to consider is your flow and heigh of your cervix. The most important thing is not to overcomplicate things. The only way to find out what size is best for you is to try one.
The small size YONI is suitable for light flow and is a great beginner's cup. The regular size YONI holds slightly more fluid and can, therefore, be better for a heavier flow.
If you have a low-sitting cervix, we suggest the small YONI as it is slightly shorter.
Some other things that you could consider when choosing a size are:
Lifestyle: If you're living an active lifestyle, or are a kegel gold medalist consider using the small YONI.
Age: For teens and younger menstruators, the small YONI can sometimes be easier to insert.
Pregnancy: If you have had a baby, a regular-sized cup is sometimes a better fit.
How do I measure the height of my cervix?
Your cervix moves around throughout your cycle, which means that you will never know exactly where it is. Thats why theres no need to stress too much about millimetres here. What you want, is an idea.
The method we recommend for this is called 'The Finger Knuckle Method'.
Firstly, clean your hands and find a comfortable position. Secondly, gently insert your index finger into your vagina. You are looking for something that feels like the tip of your nose (go ahead, try it - we know you want to). Your cervix is firmer than your vaginal walls so you will know it when you find it.
If you can reach your cervix by the first knuckle you have a low cervix. If you reach your cervix by the second knuckle you have a medium cervix if you reach your cervix by the third knuckle (or can't reach it at all) you have a high cervix.
Generally, people with a low/medium cervix prefer a smaller sized cup while people with a medium/high cervix prefer a slightly larger sized cup.