Smartwool to Uniqlo leggings size

The short answer

Smartwool S is Uniqlo L by the two brands' own charts. 3 of 3 Smartwool sizes land on a different label at Uniqlo.

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

On 3 sizes the charts land two or more sizes from the same label. Brands do not measure the body the same way, so on those rows treat the chart answer and the same label as the two ends of a range.

Every Smartwool size read across to Uniqlo. Letter sizes on the left, Letter on the right.
Smartwool	Smartwool builds it for	Uniqlo, by chart	Same label	Uniqlo builds it for	Uniqlo also prints
S	waist 29 to 31 in, hip 36 to 38 in	L	S	waist 29.5 to 32 in, hip 39.8 to 42.3 in	not published
M	waist 32 to 34 in, hip 39 to 41 in	XL	M	waist 32 to 34.3 in, hip 42.3 to 44.5 in	not published
L	waist 35 to 37 in, hip 42 to 44 in	XXL	L	waist 34.3 to 36.5 in, hip 44.5 to 46.8 in	not published
XL	waist 38 to 40 in, hip 45 to 48 in	not made	XL	not published	not published
XXL	waist 41 to 44 in, hip 49 to 51 in	not made	XXL	not published	not published

Tinted rows change label or sit between two sizes. 2 sizes have no counterpart on the Uniqlo 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

Smartwool size guide, read on 2026-09-18.
Uniqlo size guide, read on 2026-09-18. Uniqlo on TrueToSize

Uniqlo to Smartwool