How to Pick A Menstrual Cup Size

Sizing guidelines for menstrual cups are helpful, but everyone has a unique body. So many things affect how cups fit and feel; it’s inevitable to see people find their perfect cups outside of all of the “prescribed” ideals that exist.

How do you pick the right menstrual cup size for your body when there are so many brands and options?

Reusable menstrual cups are worn in the vaginal canal and sit below the cervix. They work by creating a seal and, when worn correctly, are completely leak-free and comfortable. For a full overview of how cups work watch my “Everything you Need to Know” video.

Menstrual cups most often come in two size choices, a small or large version, but not always. Some brands have 3-4 sizes, including smaller teen options. One brand has 10! So how do you choose which size menstrual cup is best for you? Cup size should be determined only by fit, not flow. You can buy a cup because it has a high capacity but it has to also be a good fit. Do not choose a cup based solely on how much it holds unless the other attributes, like the diameter and length, are also a good fit for you.

Here’s the short answer, but it’s not an entertaining one. Skip the lesson and take the quiz on periodnirvana.com. The quiz will walk you through all of the questions my custom algorithm needs for it to match you to a cup or disc that is most likely the right size, firmness, shape, capacity, length, etc for you. And while you may be suspicious about the accuracy I have to tell you that this quiz has 6 months of logic and testing behind it. Not to mention it will ask you questions you had no idea would matter for picking a cup!

What factors influence picking a cup size

First, it’s important to know HOW cups are sized

The frustrating thing is that there is no true standardized terminology or methodology. I will say that virtually all menstrual cups determine their sizing by the diameter alone. When a cup brand says it’s a “small” it means it’s a smaller diameter in the rim (the top edge and opening of the cup.) To add to the confusion, brands have no standard naming practices for their sizes. One brand’s small is another brand’s size A. One brand’s size A is another brand’s size B. Then some size by numbers… or special codes… It’s a mess out there, y’all.

Why Cups Are Sized By Diameter

For a cup to stay in place it relies on two things: the suction it creates with the vaginal walls and your pelvic floor muscles.

Ever wonder why cups say “use our size large if you’re over 30 or have had a full-term pregnancy?” It’s because those things both affect your pelvic floor muscle tone. At a certain age our muscles relax, so they become less tight. A full-term pregnancy, even for someone in their teens, could have the same relaxing effect. So being over 30 AND/OR a full-term pregnancy puts you into the “larger diameter” size range. These sizes are often names as sizes “Large,” “2,” “B,” or “Regular.” Though some brands reverse their “A” and “B” so definitely look at listings carefully.

Exercise and Menstrual Cup Size

Your physical activity can also affect the fit of your cup. If you are someone who is very active it’s likely you’ve slowed down or reversed the relaxation of your pelvic floor muscles. For that reason, you could be over 30, or someone who had lots of pregnancies but have the vaginal muscles of an 18-year-old! Perhaps you can lift a canoe with your vagina! If you’ve had pelvic floor therapy this rationale applies to you as well.

The point is, these size guidelines on the outside of the box are basic and helpful but they aren’t rules you must follow.

On the Fence? Size Up, Not Down

When in doubt, size up. Why? Because your vagina was designed to stretch and accommodate things… things of sizes about the diameter of cups or larger.. And also MUCH larger like a baby’s head. What it’s not good at doing is clenching itself around a cup that is too narrow that wants to slip down during wear… you can’t make a cup that’s too small to fit stay in place.

Ask Yourself These Questions Before Picking Your Menstrual Cup Size

If you are deciding on a size you should ask yourself – 

• Am I under 17 and nervous about using a menstrual cup? If yes, you’re a good candidate for a teen-sized cup. But if you’re under 17 and have a heavier period or if you think you’re comfortable with the insertion of cups, you can also look at size smalls.
• Am I under 30 and have had no full-term pregnancies? If yes, you’re likely a size small.
• Did I have a full-term pregnancy (age does not matter)? If yes, you’re likely a brand’s size large.
• Am I over 30? If yes, you’re likely a brand’s size large.

Other scenarios to consider:

• Am I very physically active and do I do exercises that would tone my pelvic floor? Or, Did I go through pelvic floor therapy? If yes, you may still be in the large cup size category but could also probably still fit a size small as well. If you’re on the fence, size up.
• I just had a baby and have a size small cup at home- do I need to automatically run out and buy a size large? Not always. Before you buy another cup try the one at home first. It may still fit and work great.
• I just turned 30 years old, do I need to switch to a larger menstrual cup? No! Assuming the cup you used for your cycle in your 29th year fits you well you can continue using that cup for now. If your cup slips down during wear a larger diameter will likely help. Otherwise, use it until it’s time to replace it for other reasons.
• I have vaginismus, which menstrual cup size would be best? No matter your age or pregnancy history you should consider a teen/petite starter cup as a way to ease into an internal product. I’ve spoken with many users who have used cups successfully but there is a lot of patience and practice involved. A more petite cup will be helpful in that process.

Related Resource: How long do menstrual cups last?

I also want to mention that many users under 30 have discovered that a size large works better for them. If you are by definition a size small cup but you find a larger cup to work best there is nothing wrong with you! Everybody is different and these guidelines are there to help you but they aren’t here to dictate your choices. In the end, you know your body best. 45-year-olds with a petite build may still need a small, and an 18-year-old may find that a size large is a better fit. The sizing guidelines are helpful but everyone has a unique body. So many things affect how cups fit and feel; it’s inevitable to see people find their perfect cups outside of all of the “prescribed” ideals that exist.

Firmness, Cervix Height, and Flow

The other keys to the sizing puzzle are for the firmness of the cup – how soft or firm it feels when squeezing it in your hands – and the length of the cup itself. 

This post won’t dive into those aspects but you should always measure your cervix height before you pick a cup to make sure it’s going to fit into your vaginal canal without sticking out. I have a guide on how to measure your cervix.

There are menstrual cups for heavy flow that can give you a longer wear time. Before you buy one just be sure that the other attributes are a good fit – this is why on the quiz we ask if you want to prioritize the fit over the capacity. You can try a cup like the Merula XL simply because it holds the most but that doesn’t mean it’s going to be the best fit for you. Another option for people with a heavy period is to try a reusable menstrual disc; these hold more than most cups and are less finicky on size attributes than cups!

Take the Period Nirvana Quiz

It does sound completely overwhelming but my goal is to take that confusion out of picking your cup. Period Nirvana’s menstrual cup quiz can help you narrow down your options to ones most likely to be a good fit.

If you want to select cups and do some shopping of various brands use our chart to sort and find cups by measurements.