Old Navy to Under Armour size
The short answer
Old Navy XS is Under Armour SM by the two brands' own charts. 7 of 8 Old Navy sizes land on a different label at Under Armour.
Both brands publish the body chest each size is cut for, so every row matches a chest, not a letter.
| Old Navy | Old Navy builds it for | Under Armour, by chart | Same label | Under Armour builds it for | Under Armour also prints |
|---|---|---|---|---|---|
| XS | chest 36 to 37 in, neck 13 to 13.5 in, sleeve 31.5 to 32 in | SM | XS | chest 34 to 37 in, waist 29 to 31 in | not published |
| S | chest 38 to 39 in, neck 14 to 14.5 in, sleeve 32.5 to 33 in | MD | not published | chest 37 to 41 in, waist 31 to 34 in | not published |
| M | chest 40 to 42 in, neck 15 to 15.5 in, sleeve 33.5 to 34 in | LG | not published | chest 41 to 44 in, waist 34 to 37 in | not published |
| L | chest 44 to 46 in, neck 16 to 16.5 in, sleeve 34.5 to 35 in | XL | not published | chest 44 to 48 in, waist 37 to 41 in | not published |
| XL | chest 48 to 50 in, neck 17 to 17.5 in, sleeve 35.5 to 36 in | XXL | XL | chest 48 to 52 in, waist 41 to 45.5 in | not published |
| XXL | chest 51 to 53 in, neck 18 to 18.5 in, sleeve 36.5 to 37 in | XXL | XXL | chest 48 to 52 in, waist 41 to 45.5 in | not published |
| XXXL | chest 55 to 57 in, neck 19 to 19.5 in, sleeve 37.5 to 38 in | 3XL | 3XL | chest 52 to 56 in, waist 45.5 to 50 in | not published |
| XXXXL | chest 58 to 60 in, neck 20.5 to 21 in, sleeve 38.5 to 39 in | 4XL | 4XL | chest 56 to 60 in, waist 50 to 54.5 in | not published |
What wearers say
Charts describe a garment, not a fit. We do not collect fit reports for this category yet, so this table is the two brands' own claims and nothing more.
Sources
- Old Navy size guide, read on 2026-09-18. Old Navy on TrueToSize
- Under Armour size guide, read on 2026-09-18. Under Armour on TrueToSize