In between sizes? Choose a smaller size for a tight fit as stockings should be worn tight.
If you choose stockings too small, it could be that: the stocking is too stretched which may cause the lace collars to snap, stockings quickly rip around the toes, or will be very uncomfortable.
If you choose stockings too big they may wrinkle and won't snug well.
Sizes are based on body measurements and written in centimeters (cm), weight is in kg.