Smartwool to Under Armour leggings size

The short answer

Smartwool S is Under Armour MD by the two brands' own charts. 5 of 5 Smartwool sizes land on a different label at Under Armour.

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 Under Armour. Letter sizes on the left, Letter on the right.
Smartwool	Smartwool builds it for	Under Armour, by chart	Same label	Under Armour builds it for	Under Armour also prints
S	waist 29 to 31 in, hip 36 to 38 in	MD	not published	waist 29 to 31 in, hip 38 to 40 in	US numeric 8-10
M	waist 32 to 34 in, hip 39 to 41 in	LG	not published	waist 31 to 34 in, hip 40 to 43 in	US numeric 12-14
L	waist 35 to 37 in, hip 42 to 44 in	XL	not published	waist 34 to 37 in, hip 43 to 46 in	US numeric 16
XL	waist 38 to 40 in, hip 45 to 48 in	XXL	XL	waist 37 to 40 in, hip 46 to 49 in	US numeric 18
XXL	waist 41 to 44 in, hip 49 to 51 in	3XL	XXL	waist 40 to 43 in, hip 49 to 52 in	US numeric 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

Smartwool size guide, read on 2026-09-18.
Under Armour size guide, read on 2026-09-17. Under Armour on TrueToSize

Under Armour to Smartwool