With so many choices out there and the conflicting sizing guidelines from each brand it’s confusing to pick a menstrual cup size. But what are the sizes and which size menstrual cup will fit you best?

Menstrual Cup Sizes

Most often menstrual cups come in two sizes but some brands offer three. A small number of brands offer more options that are specialized including “low cervix” sizes. The most common option is of a “small” and “large” and while there isn’t a sizing standard you can expect that these brands size their smalls anywhere from 35-43 mm and the larger sizes around 43 mm- 48mm in diameter at the rim of the cup.

If you go by the guidelines issued by most brands of “under 30 years old and haven’t given birth- you’re a size 1 and over 30 or you have given birth, which includes any full term delivery, you’re a size 2” one brand’s smallest size can be the size of another brand’s large! Other brands like to size cups by the amount of fluid they hold and tell you to pick a larger cup if you have a heavy flow, a smaller cup if you have a lighter flow.

If we had to pick, selecting a size based on age+birth history is more accurate than selecting a cup based on flow. In the case of a person who is over 30 but who has a lighter than average flow it’s very possible if they select the smaller size for this reason and that cup isn’t wide enough in diameter to stay in place it will cause frustration for the user as the cup slips down. We stress that this is NOT a perfect guideline but is a helpful place to start when you haven’t yet tried a menstrual cup but trust your gut, always, when making your choice.

Choosing a Cup Size Based on Length

Before you consider any other factors when choosing your cup forget the “size” and start with length. A cup that is too long to fit completely inside your vagina will not work for you (yell it for the people in the back!) But how do you know how long your vagina is? You need to measure where your cervix is during your period and this can be done by taking a clean finger, inserting, and locating your cervix. It should feel like the tip of your nose. If you can’t find it that may mean you have such a high cervix it can’t be reached, this is good! That just means you can use practically any length of cup you’d like. Once you find your cervix place your thumb against your finger to mark all the length that fits inside, then remove your finger and measure to where you placed your thumb. A precise measurement is preferred to the knuckle method often depicted in sizing graphics because our fingers are different lengths.

Related: Find a Low Cervix Menstrual Cup

Choosing a Cup Size Based on Diameter

Now that you know your cervical height we can begin the task of choosing your cup’s “size.” Generally the sizes refer to the diameter of the cup and have little to do with the length, though smaller sizes are most often shorter than their larger counterparts but not always. See? Confusing!

It is true that your pelvic floor muscles tend to relax with age and/or after you’ve had a full term pregnancy. The sizing guideline  “given birth” has nothing to do with you delivering vaginally and just means your body has prepared for labor and muscles are looser after. If you delivered vaginally forget the notion that your baby blew through your vagina and left a cave behind; your vagina does stretch but it returns to a normal size. You can use that guide to decide if you are a smaller cup or larger cup but the fact is you know your body best. If you feel like you have a petite vaginal canal but you’re over 30 or you’ve had a baby, you might still use a size 1. If you know you do exercises that work the pelvic floor muscles or perhaps you have done pelvic floor therapy and understand you have a stronger pelvic floor then you can also select a size 1. For more information about pelvic floor therapy visit our friend, The Down There Doc, or look for a pelvic floor therapist near you. The difference between most sizes is pretty minimal so if you’re in doubt remember your vagina stretches but cannot “clamp down” to keep a cup in place. With that in mind perhaps a size 2 is a safer bet.

Choosing a Cup Size Based on Capacity

Now we come to the capacity factor. Most smaller cup sizes hold around 25-27 millileters, most larger cups hold around 30 milliliters. Unless you have a very very heavy flow don’t factor the capacity into your sizing option at all. Cups hold so much more than tampons that the average person won’t fill a cup in a 12 hour timeframe. It’s just a non issue to pick a cup based on capacity when the length and size matter more for the fit. That being said if you are a very heavy bleeder you can find cups with higher capacities but you will still want to account for their length. The higher capacity the cup has, often the larger it is in both diameter and length, and you need to make sure it will fit you before picking based on capacity alone.

Related: Compare high capacity cups

Picking The Most Accurate Size Cup

To make this all even more confusing I want to remind you that each brand has their own idea of what their small and large sizes are. For example, the small Super Jennie is the same diameter as the Fun Cup and Lily Cup brand’s larger size cup. It isn’t straightforward which is why using our menstrual cup comparison chart to sort by measurements such as diameter, length, or capacity is the most accurate way to find a cup, but also advanced for someone who has yet to try a cup. If you’re brand new just take our menstrual cup quiz and start with the list of recommended cups we provide you based on your answers. Knowing your cervical height is important to getting the most accurate quiz result but we also factor in what we know to be an average and point you there if you don’t know.