Gymshark to GU size

The short answer

Gymshark XS is GU M by the two brands' own charts. 6 of 7 Gymshark sizes land on a different label at GU.

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

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 Gymshark size read across to GU Japan sizing. Letter sizes on the left, Letter on the right.
Gymshark	Gymshark builds it for	GU Japan sizing, by chart	Same label	GU builds it for	GU also prints
XS	chest 37 in, waist 29.5 in	M	XS	chest 34.7 to 37.8 in, waist 29.9 to 33.1 in	not published
S	chest 39 in, waist 31.5 in	L	S	chest 37.8 to 40.9 in, waist 33.1 to 36.2 in	not published
M	chest 41 in, waist 33.5 in	XL	M	chest 40.9 to 44.1 in, waist 36.2 to 39.4 in	not published
L	chest 43 in, waist 35.5 in	XL	L	chest 40.9 to 44.1 in, waist 36.2 to 39.4 in	not published
XL	chest 45 in, waist 37.5 in	XXL	XL	chest 44.1 to 47.2 in, waist 39.4 to 42.5 in	not published
XXL	chest 47 in, waist 39.5 in	XXL	XXL	chest 44.1 to 47.2 in, waist 39.4 to 42.5 in	not published
XXXL	chest 49 in, waist 41.5 in	3XL	3XL	chest 47.2 to 50.4 in, waist 42.5 to 45.7 in	not published

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, 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.

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Sources

Gymshark size guide, read on 2026-09-18. Gymshark on TrueToSize
GU Japan sizing size guide, read on 2026-09-25.

GU to Gymshark