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About this tool
Cup size, length and firmness guidance from your age, birth history and a measured cervix height.
The Menstrual Cup Size Finder turns three separate fit decisions — diameter, length and firmness — into one starting recommendation. Diameter follows the sizing convention almost every brand publishes: the smaller size under 30 with no vaginal birth, the larger size from 30 onwards or after a vaginal birth. Length follows your measured cervix height, where under about 45 mm is a low cervix, 45 to 55 mm is average and over 55 mm is high. Firmness follows your pelvic floor, because a strong one can compress a soft cup and break its seal.
Open Menstrual Cup Size Finder on AltFTool — it loads instantly in your browser.
Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
Most sizing charts only cover diameter, which is why a correctly sized cup can still sit wrong.
A millimetre measurement or a knuckle cue puts a real number behind the length advice.
No product is recommended; you get the specification to look for on any brand's own chart.
Most brands suggest the smaller size (often labelled size 1) if you are under 30 and have not given birth vaginally, and the larger size (size 2) from 30 onwards or after a vaginal birth. A caesarean birth is normally treated as no vaginal birth, so age decides.
With clean hands, insert one finger into the vagina during your period until you feel the cervix, which is firm and rounded like the tip of your nose. Reaching it at the first knuckle is a low cervix, around 45 mm or less; the second knuckle is average, 45 to 55 mm; barely reaching or not reaching it is high, over 55 mm.
Firmer cups pop open more easily and resist being squashed, which suits a strong pelvic floor from running, lifting or pelvic floor training. Softer cups press less on the bladder and are usually more comfortable if you notice pressure or sensitivity — the trade-off is that they can be harder to open.
Many people do, but check with the clinician who fitted it first, and always break the suction seal fully before removing the cup so the strings are not pulled. This tool gives general guidance only and is not medical advice — see a clinician if you have pain, persistent leaking, or a recent gynaecological procedure.