Written and maintained by CASRAI Editorial Board
Last updated
Ring pessary sizes are given as a size number, a diameter in millimetres and a nominal diameter in inches, and the three do not line up across manufacturers. The chart below sets the ring sizes published by two manufacturers side by side, MedGyn and CooperSurgical (Milex), using each company’s own product documents. It is a reference for reading catalogue and packaging labels, not a way to pick a size: a pessary is a prescription medical device, and the size is chosen by a healthcare professional.
Ring pessary size chart in mm and inches
Rows are grouped by the nominal inch value each manufacturer lists. Diameters are in millimetres as printed by the manufacturer. A dash means that size does not appear in that manufacturer’s table.
| Nominal size (in) | MedGyn ring with support | MedGyn ring without support | Milex ring with support (fitting kit) |
|---|---|---|---|
| 2 | #1, 51 mm | #1, 51 mm | – |
| 2 1/4 | #2, 58 mm | #2, 58 mm | Size 2, 57 mm |
| 2 1/2 | #3, 62 mm | #3, 62 mm | Size 3, 64 mm |
| 2 3/4 | #4, 69 mm | #4, 70 mm | Size 4, 70 mm |
| 3 | #5, 75 mm | #5, 75 mm | Size 5, 76 mm |
| 3 1/4 | #6, 82 mm | #6, 82 mm | Size 6, 83 mm |
| 3 1/2 | #7, 90 mm | #7, 90 mm | Size 7, 89 mm |
| 3 3/4 | #8, 94 mm | #8, 94 mm | – |
| 4 | #9, 102 mm | #9, 102 mm | – |
Check your product’s labelling. The numbers above come from the manufacturers’ documents named under Sources and apply only to those product lines. The size, type and dimensions printed on the packaging or instructions for use of the exact product in your hands are the ones that count.
How to read the chart
Each cell has two parts: the manufacturer’s size designation (#4 for MedGyn, “Size 4” for Milex) and the diameter in millimetres. The left-hand column is the nominal inch value both companies use in their listings. Read across a row to see how the same nominal inch size is stated by each manufacturer.
The MedGyn page lists its rings in two families, with a supporting membrane and without, in nine sizes each. The Milex column comes from the “RING with Support” table in the CooperSurgical Milex Pessary Fitting Kit instructions for use, which covers the sizes included in the fitting kit (2 to 7), not the manufacturer’s whole range.
Who chooses the size, and what a fitting kit is
The Milex instructions for use state that the fitting kit was developed to help a healthcare professional “determine accurate pessary type and size prior to prescribing a pessary for your patient.” The same document carries the U.S. “Rx only” caution, which reads “U.S. Federal law restricts this device to sale by or on the order of a physician”. MedGyn says its range of sizes lets “clinicians” customise the fit for individual anatomy and comfort.
The instructions for use also say not to assume that a replacement will always be the same size as the previous one. This page therefore gives no rule for selecting a size and no fitting steps; those belong to a clinician working from the manufacturer’s instructions.
Equivalence notes: numbers, millimetres and inches
Size number is not a universal unit
A size number identifies a size within one manufacturer’s line. MedGyn #2 is listed at 58 mm and Milex size 2 at 57 mm; MedGyn #3 is 62 mm against 64 mm for Milex size 3; MedGyn #7 is 90 mm against 89 mm for Milex size 7. The differences in the chart are one to two millimetres, so the same number does not mean the same diameter from one catalogue to another.
Inches and millimetres are nominal
Both manufacturers print inches and millimetres, but the inch figure is a nominal label. The Milex table pairs 2 1/2 inches with 64 mm, while MedGyn pairs 2 1/2 inches with 62 mm. When a document gives both, the millimetre value is the more precise one to compare.
With and without support
MedGyn lists a ring with support and a ring without support at the same size number. For eight of nine sizes the millimetre value is identical. For #4 the with-support ring is listed at 69 mm and the without-support ring at 70 mm; the product page does not explain the difference, so the chart shows both exactly as printed.
Common mix-ups
- Size number versus diameter. “Size 5” names a position in one manufacturer’s series. The diameter in millimetres is the measurement.
- One brand’s number used for another brand’s product. The chart shows the same number can mean 1 to 2 mm more or less depending on the maker.
- Kit sizes versus the full range. The Milex fitting kit table covers sizes 2 to 7. MedGyn lists sizes #1 to #9. A size missing from one document is not evidence that it does not exist in that brand’s wider range.
- Ring type versus ring size. Rings with and without support, and other shapes such as donut or cube, have their own size tables in the manufacturers’ documents. The values in this chart are for rings only.
- Material assumptions. MedGyn describes its ring as medical-grade silicone and latex-free, and the Milex instructions carry a symbol stating the device is not made with natural rubber latex. Check the label of the product you have rather than assuming.
For the medical specialties that work with these devices, see the guides to obstetrics and gynecology and urology. For how problems with marketed devices are tracked in the United States, see medical device reporting (MDR).
FAQ
Are pessary sizes the same across brands?
No. In the published ring tables of these two manufacturers, the same size number corresponds to diameters that differ by 1 to 2 mm (for example #3 is 62 mm for MedGyn and 64 mm for Milex).
What does the number on a ring pessary mean?
It is the manufacturer’s size designation within its own product line. The millimetre diameter printed beside it is the dimension to compare.
Who decides which pessary size is used?
A healthcare professional. The Milex instructions for use describe their fitting kit as a tool for a healthcare professional to determine pessary type and size before prescribing, and the device carries the U.S. “Rx only” restriction.
Is a ring pessary with support a different size from one without?
In MedGyn’s listing the sizes are the same except #4, which is 69 mm with support and 70 mm without.
Sources
- MedGyn, “MedGyn Ring Pessary” product page, https://www.medgyn.com/product/medgyn-ring-pessary/ (ring with and without support, sizes #1 to #9; checked 2026-10-29).
- CooperSurgical, “Milex Pessary Fitting Kit, Fitting Instructions for the Healthcare Professional” (instructions for use, PDF), https://www.coopersurgical.com/wp-content/uploads/2025/12/Pessary-Fitting-Kit-Instructions-for-Use.pdf (RING with Support kit sizes, Rx only caution; checked 2026-10-29).
This page is general product information. It is not medical advice and does not describe fitting, insertion or removal. Talk to a qualified clinician about any pessary.
