Let’s talk about the question that probably brought you here: What size menstrual cup do I need?
I know it feels confusing. You’re scrolling through websites, seeing “Size 1” and “Size 2,” or brands asking if you’re over 30 or have had a baby, and you’re thinking, “Wait, what does my age have to do with my period?”
Here’s what I want you to know right up front: There is no single “correct” size. Many people can actually use different sizes at different times—even during the same period. Most beginners fall somewhere between two options, and honestly? Most people get it right on the first or second try.
The confusing part is that most companies offer just 2 sizes to fit most bodies (the difference is usually in the diameter), but there’s no standard between brands. So the variants are actually infinite. But don’t let that overwhelm you. We’re going to break this down in a way that actually makes sense.
The 3 Factors That Actually Matter
Forget the random internet advice about your flow or whether you do yoga. Here’s what really determines your cup size:
1. Cervix Height (Length)
This is about how high or low your cervix sits in your vaginal canal. Think of it like this: you don’t want a cup that’s too tall (uncomfortable) or too short (won’t catch everything).
How to measure: Insert one or two clean fingers into your vagina during your period (your cervix position changes throughout your cycle, so day 1 or 2 is best). You’re feeling for something that feels
kind of like the tip of your nose—firm but a bit soft.
- High cervix: Can’t reach it easily with your fingers → You can wear longer cups
- Average cervix: Fingers go in a good way but you can reach it → Most standard cups work
- Low cervix: You reach it almost immediately, just inside the opening → You need shorter cups
2. Pelvic Floor Tone (Diameter)
This is where that “over 30 or had a baby” rule comes from—but it’s way more nuanced than most websites make it sound.
Your pelvic floor muscles naturally lose some tone over time. It’s gradual, not something that happens overnight. Someone just had to draw a line in the sand, and science said, “Generally speaking, that happens around 30.”
Here’s the real guideline:
- Smaller diameter: Usually best if you’re under 30 AND haven’t had a full-term pregnancy (37+ weeks)
- Larger diameter: Usually best if you’re over 30 OR have had a full-term pregnancy
Important clarifications:
- “Full-term pregnancy” means both C-sections and vaginal births. It’s not about what came out of your vagina—it’s about your body preparing for labor and your pelvic floor muscles relaxing during pregnancy.
- Being 29 vs. 30 doesn’t magically change your body. This is just a helpful starting point.
- Your sexual history doesn’t matter at all. Not how many partners, not what you’ve put in there, none of it. This is purely about muscle tone.
But wait—muscles can be worked out, right? YES. If you’re over 30 but very physically active (strength training, Pilates, pelvic floor therapy), your muscles might still be quite toned. You could totally still use a smaller diameter cup. This is just a guideline, not a rule.
3. Cup Firmness
This doesn’t determine your size, but it works hand-in-hand with diameter:
- Firmer cups: Better for active people because they resist the pressure from toned pelvic floor muscles and stay sealed
- Softer cups: More comfortable for many people, especially if you have bladder sensitivity
If you have strong pelvic floor muscles, you’ll probably want a firmer cup in addition to considering diameter.
Smaller Size (Size 1, Small, A)
Usually best for:
- Under 30 years old
- No full-term pregnancies
- Petite build or naturally narrow anatomy
- Very active with toned pelvic floor
Medium/Standard Size
Usually best for:
- Most beginners who fall in the “average” zone
- Over 30 OR have had a full-term pregnancy
- Moderate activity level
Larger Size (Size 2, Large, B)
Usually best for:
- Over 30 AND have had a full-term pregnancy
- Postpartum (after recovery)
- Lower pelvic floor tone
Let’s bust some myths:
- “I’m petite, so I need the smallest cup” → Not necessarily. Your external body size doesn’t dictate your internal anatomy.
- “I had a C-section, so the size rules don’t apply” → Actually, they do. Your body still prepared for labor.
- “I’m 45 and think I have a tiny vagina” → You might be right! These are guidelines. You know your body best.
What If You’re Between Sizes?
This is SO common, and honestly, this is where I want to give you the most helpful advice.
When to size down:
- You’re very active and have a toned pelvic floor
- You’re on the younger side of 30 or just barely past full-term pregnancy
- You feel “tight” down there
When to size up:
- You’re on the fence and truly can’t decide
- You’re in your 40s+
- You’ve had multiple pregnancies
Here’s why I usually suggest sizing up when you’re truly unsure: Your vagina is designed to stretch and accommodate. But it can’t clinch down on something that’s too narrow. A cup that’s slightly too small will slowly slip throughout the day (not fun), while a cup that’s slightly too large will just… stretch you a tiny bit, which your body is built to do.
My personal advice: If you’re really in doubt, you can get both sizes—or if you want to start with just one, get the bigger one first. Even if it’s not perfect for you at the beginning, it might work later (like postpartum, or as you age, or on heavier flow days). Most brands offer two sizes for exactly this reason.
Firmness can help compensate: If you size up but worry it’ll slip, try a firmer cup. If you size down but worry about comfort, try a softer one.
First-Time Tips to Make Any Size Work Better
- Try different folds: The punch-down fold or C-fold can make insertion easier with any size
- Relax: I know, easier said than done. But tension makes everything harder. Take your time, maybe try in the shower.
- Give it a real trial: Test your cup for at least 2-3 cycles before deciding it doesn’t work. The first time is a learning curve for everyone.
- Troubleshooting is normal: If the cup won’t unfold, try pressing against the vaginal wall or pushing up from the bottom. If it still won’t open, it might be too large for you.
Common Beginner Mistakes
Let’s normalize the learning process:
Choosing only based on age. The “over 30” rule is a starting point, not gospel. Activity level and pregnancy history matter too.
Panicking on the first cycle. Your first time using a cup is going to feel weird. That’s normal. Weird doesn’t mean wrong.
Giving up too early. Most people need 2-3 cycles to really get the hang of it. Don’t toss your cup after one bad experience.
Comparing too much online. Everyone’s body is different. What works for someone else might not work for you, and that’s okay.
Ignoring cervix height. Diameter gets all the attention, but length matters just as much (if not more). A cup that’s too long will be uncomfortable no matter what diameter it is.
You’ve Got This
Choosing a menstrual cup size isn’t about getting it perfect on the first try—it’s about finding what works for your body. And guess what? Your body might change over time, and that’s totally fine too.
Start with the guidelines (cervix height + the age/pregnancy factors), trust your gut about your own body, and remember that most people figure it out within a try or two. You’re not behind, you’re not doing it wrong, you’re just learning.
And if you need more help, these guides might be useful next:
- How to insert and remove a menstrual cup (beginner guide)
- Best folds for different cup sizes
- Understanding cup firmness
You’re making a great choice for your body and the planet. Take it one step at a time, and be patient with yourself.
Have questions or want to share your experience? Drop a comment below—I’d love to hear from you!