Period underwear size guide: getting the fit right
A plain guide to choosing a size in YOYI FASHION period underwear, teen briefs, swim bottoms and cotton packs.
Measure hips, not guesses
Take a tape around the fullest part of your hips. Our size charts on the listing are built on that number.
Snug is the goal
A backup pair works when the lining sits close. If you are between sizes and want the lining held firmly, choose the smaller one.
Teen sizes go by age band
XS covers 8 to 10 years, S 10 to 12, M 12 to 14, L and XL 14 to 16 — then check the hip measurement to confirm.
Cotton packs use numbers
String bikinis and thongs are sized 5 to 9. Size 5 fits a 25 to 26 inch waist, size 7 a 29 to 30 inch waist, size 9 a 33 to 34 inch waist.
Wearers tell us the cotton styles can run a little small and that the briefs shrink in a dryer — another reason to air dry.