Onzie to Sweaty Betty leggings size

The short answer

Onzie X/S is Sweaty Betty XS by the two brands' own charts. 5 of 5 Onzie sizes land on a different label at Sweaty Betty.

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 Sweaty Betty. Letter sizes on the left, Letter on the right.
Onzie	Onzie builds it for	Sweaty Betty, by chart	Same label	Sweaty Betty builds it for	Sweaty Betty also prints
X/S	waist 24 to 26 in, hip 33 to 35 in	XS	not published	waist 25 in, hip 36 in	US numeric 4
S/M	waist 26 to 28 in, hip 36 to 38 in	S	not published	waist 27 in, hip 38 in	US numeric 6
M/L	waist 28 to 31 in, hip 38 to 40 in	M	not published	waist 29 in, hip 40 in	US numeric 8
L/L	waist 31 to 33 in, hip 40 to 42 in	L or XL	not published	waist 31 in, hip 42 in	US numeric 10
XL	waist 34 to 37 in, hip 43 to 45 in	XXL	XL	waist 36 in, hip 46.5 in	US numeric 14
1X	waist 38 to 40 in, hip 46 to 48 in	not made	not published	not published	not published

Tinted rows change label or sit between two sizes. 1 sizes have no counterpart on the Sweaty Betty chart. 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.
Sweaty Betty size guide, read on 2026-09-17. Sweaty Betty on TrueToSize

Sweaty Betty to Onzie