GU to Old Navy size
The short answer
GU M is Old Navy XS by the two brands' own charts. 5 of 5 GU sizes land on a different label at Old Navy.
Both brands publish the body chest each size is cut for, so every row matches a chest, not a letter.
On 5 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.
| GU Japan sizing | GU builds it for | Old Navy, by chart | Same label | Old Navy builds it for | Old Navy also prints |
|---|---|---|---|---|---|
| XS | chest 29.9 to 33.1 in, waist 25.2 to 28.4 in | not made | XS | not published | not published |
| S | chest 31.5 to 34.7 in, waist 26.8 to 29.9 in | not made | S | not published | not published |
| M | chest 34.7 to 37.8 in, waist 29.9 to 33.1 in | XS | M | chest 36 to 37 in, neck 13 to 13.5 in, sleeve 31.5 to 32 in | not published |
| L | chest 37.8 to 40.9 in, waist 33.1 to 36.2 in | S | L | chest 38 to 39 in, neck 14 to 14.5 in, sleeve 32.5 to 33 in | not published |
| XL | chest 40.9 to 44.1 in, waist 36.2 to 39.4 in | M or L | XL | chest 40 to 42 in, neck 15 to 15.5 in, sleeve 33.5 to 34 in | not published |
| XXL | chest 44.1 to 47.2 in, waist 39.4 to 42.5 in | L | XXL | chest 44 to 46 in, neck 16 to 16.5 in, sleeve 34.5 to 35 in | not published |
| 3XL | chest 47.2 to 50.4 in, waist 42.5 to 45.7 in | XL | XXXL | chest 48 to 50 in, neck 17 to 17.5 in, sleeve 35.5 to 36 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
- GU Japan sizing size guide, read on 2026-09-25.
- Old Navy size guide, read on 2026-09-18. Old Navy on TrueToSize