Are you experiencing leaks? Discomfort? Or do you feel like your cup is "floating around"?
Cup size is often blamed. Yet with internal period protection, the logic isn't the same as with clothing. Thanks to the elasticity of the vagina, a cup is almost never "too small" or "too large" in diameter — but it can be in terms of capacity.
Here are the telltale signs to determine whether you need to change model.
Table of contents
1- The Quick Diagnosis (Symptom table)
Don't overcomplicate it. Here's how to interpret your experience:
| Symptom | The real problem | The solution |
|---|---|---|
| Leaks when it's FULL | Too small in capacity. | Move up a size (M or L) for longer wear time. |
| Almost empty after 6 hours | Too large in capacity. | Move down a size (S or M) to limit air inside (safety). |
| Pain on insertion / Discomfort | Specific context (dyspareunia / beginner). | Choose size S for physical and psychological comfort. |
| It slips / It moves down | Pelvic floor issue (not size). | Don't go bigger! Work on strengthening your pelvic floor. |
👉 Not sure why it's leaking? Check our troubleshooting guide first: My cup is leaking — why?
2- Case 1: My cup is "Too Small" (Overflow)
This is the most common case. We're not talking about diameter (the vagina adapts) — we're talking about reservoir capacity.
If you need to empty your cup every 2 or 3 hours, it's reaching its limit. Your flow is heavier than the cup's capacity.
- The cause: Naturally heavy flow, or a contraception change (copper IUD/coil).
- The solution: Move up to the next size.
3- Case 2: My cup is "Too Large" (The Myth)
Let's be clear: anatomically, a cup is almost never "too large". The vagina is one of the most elastic tissues in the human body (it's designed to allow a baby to pass through!). It adapts without difficulty to any cup diameter, even Size L (46mm).
However, there are two situations where going down a size is recommended:
A. The hygiene concern (Too much air)
If after 6 hours of wear your cup is barely half full, it is oversized for your flow.
Why does this matter? It means there is a significant amount of air inside. Oxygen promotes bacterial growth. To minimise the risk of Toxic Shock Syndrome (TSS), a smaller, better-filled cup with less stagnant air is preferable.
B. Comfort and personal history
While the vaginal canal is elastic, the vaginal entrance (the vestibule) can be more sensitive.
- No previous vaginal intercourse: If you have never experienced vaginal penetration, inserting a wider diameter may feel daunting or uncomfortable at the entrance. A Size S or M is often a more reassuring starting point.
- Pain (dyspareunia): If you typically experience pain during intercourse or insertion, choose a smaller size to reduce pressure on the vestibular area.
4- Case 3: My cup slips (The "too wide" myth)
This is the most persistent misconception: "I've given birth / I'm 30, so my vagina is wide, so the cup falls out."
This is FALSE.
Anatomically, the vaginal walls are always in contact with each other at rest (it is a virtual cavity). There is no "empty
space" for the cup to float in.
If your cup moves down on its own:
- It's not because it's too small.
- It's because your pelvic floor (the muscular hammock) lacks tone and is no longer holding it in place.
⚠️ The mistake to avoid: Going up a size to "fill the gap". This won't solve the problem and will mask an underlying health concern.
👉
The right approach: See a midwife or pelvic floor physiotherapist for rehabilitation. (Read our guide: Everything about the pelvic floor).
In short: Choose your size based on your FLOW (S, M or L), not the width of your vagina. And if it slips, head to a pelvic floor physio!
