Unlike menstrual cups which are sized based on your pelvic floor toneness and are primarily selected by their diameter and length, menstrual discs are almost "one size fits most." However, the menstrual disc market is much smaller than the cup market, and each disc manufacturer has taken a different approach to sizing. Some, like Nixit and Cora, have chosen a one-size-fits-all approach by picking a diameter and volume that meets the average body. Other manufacturers, notably Lumma, have created multiple sizes of discs based on your cervix height.
What Disc Size Is Right For Me?
You should start by measuring your cervix. Your cervix height does change during menstruation, and it’s best to measure while on your period for the most accurate measurement. You can measure your cervix by inserting your finger and feeling around -- your cervix will feel round and have the same firmness as the tip of your nose. Measure how deep your finger went into your vagina. You can find our "how to measure your cervix" guide by clicking this link.
I have a High Cervix
For high-cervix users, the best menstrual disc are those with a diameter greater than 65mm. Products that fit this are the Nixit and Lumma High. Lumma High is especially good for those with a high cervix because it's the only disc with a long stem that can make reaching it for removal easier.
I have an Average or Low Cervix
For low and average height cervix users, the best menstrual disc would be those with a smaller diameter. Products that fit this criteria are the Lumma Medium, Cora Disc, and Lumma Short. Even if your cervix is average or lower than average the larger discs like Cora or Nixit might still fit because of their flat shape.
I have a Tilted Cervix
If your cervix is retroflexed (facing the back wall of the vagina) a disc may be harder to use or impossible. If the disc cannot get under and past the cervix to properly tuck you will experience leaking. Most people only know they have a retroflexed uterus through being told by a care provider. If there is enough space for the disc to slip under the cervix it may still work; you will need to "scoop" the disc around the cervix during insertion, which is hard to do when you can't see inside your body. Menstrual cups, which are worn below the cervix, are usually less affected by tilts of any direction for this reason.
The menstrual disc market is not very large, and the variety of products is likewise small. There are a handful of innovations that might influence your purchase beyond disc size (measured in its diameter). The Lumma discs are the only ones to offer a ‘string’ to help find and dislodge the disc without requiring as much internal reach. The Cora Disc has a notch that helps your finger grip the edge of the disc during removal without having to loop your fingertip over the edge of the disc. The Cora Disc's removal notch has been known to rotate during wear, so if you're 100% relying on this to remove it that is a consideration. Another outlier is the Ziggy disc (not sold by Period.Shop) which is one-sized but also oblong (not perfectly round), which can help provide a better seal for users who experience leaks with round discs (not something you can test for without trying first).
Can I be sure a disc will work before buying one?
Every person’s body is unique, and while cervix height is the best indicator of a proper fit it is not fail-proof. One trick is to try a lower-cost disposable disc (Flex Disc) to determine if the size and round shape work for your body. If you are trying a disposable disc first keep in mind that these are much firmer and more rigid, because of their plastic rims, than silicone discs. If you enjoyed your experience with the disposable the closest size and firmness to the Flex or SoftDiscs is the Lumma High. Another consideration is practice -- where you could experience issues that you associate to incorrect sizing could be related to improper placement. The biggest mistake made in disc placement is not properly pushing the disc behind the pubic bone.
You can find an entire collection of trusted menstrual disc brands at Period.Shop.