Smartwool to Old Navy leggings size

The short answer

Smartwool S is Old Navy M by the two brands' own charts. 4 of 5 Smartwool sizes land on a different label at Old Navy.

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

Every Smartwool size read across to Old Navy. Letter sizes on the left, Letter on the right.
Smartwool	Smartwool builds it for	Old Navy, by chart	Same label	Old Navy builds it for	Old Navy also prints
S	waist 29 to 31 in, hip 36 to 38 in	M	S	waist 29 to 30 in, hip 39.5 to 40.5 in	US numeric 8-10
M	waist 32 to 34 in, hip 39 to 41 in	L	M	waist 31.5 to 33.5 in, hip 42 to 44 in	US numeric 12-14
L	waist 35 to 37 in, hip 42 to 44 in	XL	L	waist 36.3 to 39 in, hip 46.5 to 49 in	US numeric 16-18
XL	waist 38 to 40 in, hip 45 to 48 in	XL	XL	waist 36.3 to 39 in, hip 46.5 to 49 in	US numeric 16-18
XXL	waist 41 to 44 in, hip 49 to 51 in	2X	XXL	waist 42 to 44.3 in, hip 51.5 to 53.8 in	US numeric 20-22

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

Smartwool size guide, read on 2026-09-18.
Old Navy size guide, read on 2026-09-17. Old Navy on TrueToSize

Old Navy to Smartwool