If you’re trying to figure out which menstrual disc to buy—or you already bought one and it’s not working—you’re probably drowning in conflicting advice.
“Get a bigger disc for a high cervix.”
“Get a smaller disc if it keeps slipping.”
“One size fits most!”
Here’s the truth: “one size fits most” is misleading. Discs come in different diameters, different firmness levels, and different lengths. And what works for your cervix height might not work for your pubic bone shape or your body’s specific anatomy.
This guide will help you understand what actually matters when choosing a disc, what the numbers mean, and how to troubleshoot if your first (or second, or third) disc isn’t working.
Why “One Size Fits Most” Is Misleading
Most disc brands market themselves as “one size fits most” because discs sit in the vaginal fornix (the space behind your cervix and above your vaginal canal), which is generally similar in size across many bodies.
But here’s what they don’t tell you:
- Diameter matters. Even a 1-2mm difference can mean the difference between a disc that stays put and one that pops out constantly.
- Firmness matters. A soft disc behaves completely differently than a firm one.
- Your pubic bone shape matters. If your pubic bone is shallow or less pronounced, even a “perfect” size disc might not stay tucked.
- Your cervix height still matters—not for capacity, but for insertion technique and comfort.
So yes, many people can use a “standard” disc. But plenty of people can’t. And that’s not a failure—it’s just anatomy.
Disc Diameter: What 68mm vs. 70mm Actually Feels Like
Disc diameter is measured across the rim at its widest point. Most discs fall between 60mm and 70mm.
Common Disc Sizes:
- Small: 60-64mm (Saalt Small, Lumma Small, Moonthlies Small)
- Medium/Standard: 65-68mm (Cora, Hello Disc, Saalt Regular)
- Large: 69-70mm (Flex, Softdisc, Nixit, Lumma High)
How to Tell If Your Disc Is Too Big
What it feels like:
- The disc pops out of place easily, especially when you stand up after sitting
- It feels “springy” or like it’s under pressure
- You feel a gush of blood as it suddenly untucks from behind your pubic bone
- It’s difficult to get it to stay tucked initially
- The middle of the disc doesn’t fully open—it stays crumpled or folded
Why this happens:
A disc that’s too large doesn’t have enough space to sit comfortably. Your body is trying to hold it in place, but there’s too much material, so it keeps popping out like a loaded spring.
How to Tell If Your Disc Is Too Small
What it feels like:
- The disc feels like it’s “floating” or not making good contact
- It slips down gradually throughout the day (not a sudden pop)
- You have steady, slow leaking even when the disc is in the right position
- When you remove it, there’s blood both inside AND outside the disc (meaning your cervix isn’t fully covered)
Why this happens:
A disc that’s too small doesn’t create enough contact with your vaginal walls or doesn’t fully cover your cervix, so blood leaks around it.
The Confusing Part: Both Can Leak
This is what makes disc sizing so frustrating. A disc that’s too big will leak (because it pops out of place). A disc that’s too small will also leak (because it doesn’t cover your cervix).
The key difference:
- Too big = sudden gush when it pops out
- Too small = slow, steady leak while it’s still in place
Firmness: Why It Matters More Than You Think
Firmness affects how the disc behaves inside your body.
Firmer Discs (Flex, Softdisc, Pixie)
Pros:
- Easier to insert (they hold their shape during insertion)
- Pop open more easily once inside
- Stay in place more securely
- Less likely to collapse or fold unexpectedly
Cons:
- Can cause discomfort or pressure on your bladder, urethra, or pubic bone
- May trigger cramping if the firm rim presses on your cervix
- More “springy” and likely to pop out if the size is even slightly too large
Best for:
- People who need a disc that’s easy to insert and stays put
- People who don’t have bladder sensitivity
Softer Discs (Nixit, Cora Soft, Lumma, Hello Disc)
Pros:
- More comfortable for most people
- Conforms to your body shape
- Less pressure on the bladder or pubic bone
- Gentler on sensitive anatomy
Cons:
- Harder to insert (they can fold or bunch up during insertion)
- May not pop open as easily
- Can be trickier to tuck behind the pubic bone
- Might slip out more easily if it’s slightly too large
Best for:
- People with bladder sensitivity or pelvic floor issues
- People who find firm discs uncomfortable
- People willing to take extra time with insertion
Cervix Height: Does It Actually Matter for Discs?
Here’s where disc advice gets confusing. With cups, cervix height is critical because the cup sits lower in the vaginal canal. But with discs, your cervix height matters less for capacity and more for insertion technique and removal.
If You Have a Low Cervix (1-2 knuckles deep)
What works:
- Smaller diameter discs (60-64mm) are often easier to fit
- Shorter discs with removal tabs (Hello Disc, Lumma, Pixie)
- Softer discs that conform to limited space
Insertion tip:
You might need to insert the disc straight up instead of angling back. Softer discs especially can bunch up in front of a low cervix if you angle too far back.
Removal tip:
Use the “thumb trick”—insert your thumb (not fingers) to reach the rim and pop it out from behind your pubic bone. This works better than trying to hook it with a finger.
If You Have a High Cervix (can’t reach it easily)
What works:
- Any diameter can work, but you might prefer slightly larger discs (68-70mm) for better coverage
- Focus on firmness more than size—firmer discs are easier to insert when you can’t feel your cervix
- Discs with longer bodies or removal tabs for easier reach
Insertion tip:
Push the disc all the way back and down until it physically can’t go any further. Don’t worry about angling too much—let the disc follow the natural shape of your vaginal canal. It will scoop under your cervix on its own if you push it far enough.
Removal tip:
Bear down to bring the disc lower before trying to remove it. If you still can’t reach it, wait 15-20 minutes after waking up (your cervix is often highest in the morning).
If You Have an Average Cervix (2-3 knuckles deep)
What works:
- Most standard discs (65-68mm)
- Medium firmness discs
- Pretty much any disc, honestly—you’re in the “Goldilocks zone”
Pubic Bone Shape: The Hidden Factor
Your pubic bone is what holds the disc in place. If you have a prominent, deep pubic bone, discs will stay tucked easily. If you have a shallow or less pronounced pubic bone, discs may slip more easily—no matter what size you use.
Quick Self-Check
Insert a clean finger and feel for the ridge of bone at the front of your vaginal canal (about 1-2 inches in).
- Can you feel a clear “shelf” or ledge? → You probably have a good pubic bone for discs
- Is it more subtle or hard to feel? → You might struggle with discs slipping, even with the right size
If discs keep slipping despite trying multiple sizes:
Your pubic bone shape might not be ideal for discs. A menstrual cup (which relies on muscle tone instead of the pubic bone) might work better for you.
Simple Decision Flow: Which Disc Should You Try?
Start Here: What’s Your Cervix Height?
Low cervix (1-2 knuckles):
- Try: Saalt Small (64mm), Lumma Small (60mm), Moonthlies Small
- Avoid: Very large discs (69-70mm)
Average cervix (2-3 knuckles):
- Try: Cora (68mm), Hello Disc (68mm), Saalt Regular (66mm)
- Most standard discs will work
High cervix (can’t reach it):
- Try: Any size, but consider Nixit (70mm), Lumma Medium/High, or Flex for easier insertion
- Focus on firmness more than size
Then: Troubleshoot Based on What’s Happening
If your disc pops out suddenly:
- Cause: Too big
- Try: Size down 1-2mm
If your disc leaks slowly but stays in place:
- Cause: Too small OR not behind your cervix
- Check: Feel for your cervix through the disc basin. If it’s not covered, reinsert. If it IS covered, size up.
If your disc causes cramping or bladder pressure:
- Cause: Too firm OR too large
- Try: A softer disc in the same size, or size down
If your disc auto-dumps constantly (sneezing, standing, moving):
- Cause: Too large
- Try: Size down 1mm
If your disc won’t stay open or keeps folding inside:
- Cause: Too soft OR too large
- Try: A firmer disc OR size down
If you can’t reach your disc for removal:
- Cause: High cervix + short fingers
- Try: A disc with a removal tab OR bear down before trying to remove
The Cervix-Changes-During-Your-Cycle Problem
Here’s something that complicates everything: your cervix moves throughout your cycle.
Many people find that a disc that works perfectly on day 1 doesn’t work on day 3. Or a disc that fits great one cycle suddenly starts slipping the next.
What to Do About It
Option 1: Use different sizes for different days
Some people keep a small disc for low-cervix days and a regular disc for high-cervix days. It sounds excessive, but if you already own both, why not?
Option 2: Stick with the size that works on your heaviest days
Even if it’s not perfect every day, prioritize the days when you need it most.
Option 3: Accept some auto-dumping or minor leaks
If your disc is close-but-not-perfect, wearing period underwear as backup might be easier than buying multiple discs.
What If You’ve Tried Everything and Discs Still Don’t Work?
Sometimes, despite trying multiple sizes, firmness levels, and techniques, discs just don’t work for your body.
Reasons discs might not work:
- Your pubic bone is too shallow to hold a disc in place
- Your cervix is very low or tilted in a way that doesn’t leave enough space
- You have pelvic floor issues that make discs uncomfortable
- Your anatomy just doesn’t accommodate the disc shape
What to try instead:
- Menstrual cups (different shape, relies on muscle tone)
- Period underwear or reusable pads
- A combination of products for different flow days
Not every product works for every body. It’s not a personal failure—it’s just anatomy.
Final Thoughts
Choosing the right menstrual disc is part science, part trial and error. Cervix height gives you a starting point, but diameter and firmness are just as important—and sometimes more important.
If your first disc doesn’t work, don’t give up. Try a different size or firmness before deciding discs aren’t for you. Even a 1mm difference in diameter can completely change how a disc fits.
And if you’ve tried three or four discs and nothing works? That’s okay too. You gave it a fair shot, and there are plenty of other great period products out there.
What’s your disc sizing story? Have you found your Goldilocks fit, or are you still searching?