Onzie to Spanx leggings size

The short answer

Onzie X/S is Spanx XS by the two brands' own charts. 4 of 6 Onzie sizes land on a different label at Spanx.

Both brands publish the body waist each size is cut for, so every row matches a waist, not a tag.

Every Onzie size read across to Spanx. Letter sizes on the left, Letter on the right.
Onzie	Onzie builds it for	Spanx, by chart	Same label	Spanx builds it for	Spanx also prints
X/S	waist 24 to 26 in, hip 33 to 35 in	XS	not published	waist 25 to 27 in, hip 34 to 36 in	US numeric 0-2
S/M	waist 26 to 28 in, hip 36 to 38 in	XS	not published	waist 25 to 27 in, hip 34 to 36 in	US numeric 0-2
M/L	waist 28 to 31 in, hip 38 to 40 in	M	not published	waist 29 to 31 in, hip 38 to 40 in	US numeric 8-10
L/L	waist 31 to 33 in, hip 40 to 42 in	L	not published	waist 31 to 33.5 in, hip 40 to 42.5 in	US numeric 12-14
XL	waist 34 to 37 in, hip 43 to 45 in	XL	XL	waist 33.5 to 36 in, hip 42.5 to 45 in	US numeric 16
1X	waist 38 to 40 in, hip 46 to 48 in	1X	1X	waist 36 to 39 in, hip 45 to 48 in	US numeric 18-20

Tinted rows change label or sit between two sizes. Read from the two charts only; no formula and no averaging.

What wearers say

Charts describe a garment. People who own both brands describe a fit, and their answer ranks above this table once five of them stand behind it. Pick your size in the converter to see whether there are enough yet.

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Sources

Onzie size guide, read on 2026-09-18.
Spanx size guide, read on 2026-09-18. Spanx on TrueToSize

Spanx to Onzie