Reiss to Arc'teryx clothing size

The short answer

Reiss 8 is Arc'teryx XS by the two brands' own charts.

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

Every Reiss size read across to Arc'teryx. UK sizes on the left, Letter on the right.
Reiss	Reiss builds it for	Arc'teryx, by chart	Same label	Arc'teryx builds it for	Arc'teryx also prints
4	bust 31 in, waist 24 in, hip 34 in	not made	XS	not published	not published
6	bust 32 in, waist 25 in, hip 35 in	not made	XS	not published	not published
8	bust 33 in, waist 26 in, hip 36 in	XS	S	bust 33.1 in, waist 26.8 in, hip 36.2 in	not published
10	bust 35 in, waist 28 in, hip 38 in	S	S	bust 35 in, waist 28.7 in, hip 38.2 in	not published
12	bust 37 in, waist 30 in, hip 40 in	M	M	bust 37 in, waist 30.7 in, hip 40.2 in	not published
14	bust 39 in, waist 31.5 in, hip 42 in	L or M	M	bust 40.2 in, waist 33.9 in, hip 43.3 in	not published
16	bust 41 in, waist 33.5 in, hip 44 in	L	L	bust 40.2 in, waist 33.9 in, hip 43.3 in	not published
18	bust 43 in, waist 36 in, hip 46.5 in	XL	L	bust 44.1 in, waist 37.8 in, hip 47.2 in	not published

Tinted rows change label or sit between two sizes. 2 sizes have no counterpart on the Arc'teryx chart. 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

Reiss size guide, read on 2026-09-18.
Arc'teryx size guide, read on 2026-09-18.

Arc'teryx to Reiss