Arc'teryx to Reiss clothing size

The short answer

Arc'teryx M is Reiss 12 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 Arc'teryx size read across to Reiss. Letter sizes on the left, UK on the right.
Arc'teryx	Arc'teryx builds it for	Reiss, by chart	Same label	Reiss builds it for	Reiss also prints
XS	bust 33.1 in, waist 26.8 in, hip 36.2 in	8	not published	bust 33 in, waist 26 in, hip 36 in	US 4 · Letter S · FR 38 · IT 40 · AU 8 · EU (as printed) 36
S	bust 35 in, waist 28.7 in, hip 38.2 in	10	not published	bust 35 in, waist 28 in, hip 38 in	US 6 · Letter S · FR 40 · IT 42 · AU 10 · EU (as printed) 38
M	bust 37 in, waist 30.7 in, hip 40.2 in	12	not published	bust 37 in, waist 30 in, hip 40 in	US 8 · Letter M · FR 42 · IT 44 · AU 12 · EU (as printed) 40
L	bust 40.2 in, waist 33.9 in, hip 43.3 in	16 or 14	not published	bust 41 in, waist 33.5 in, hip 44 in	US 12 · Letter L · FR 46 · IT 48 · AU 16 · EU (as printed) 44
XL	bust 44.1 in, waist 37.8 in, hip 47.2 in	not made	not published	not published	not published
XXL	bust 48 in, waist 41.7 in, hip 51.2 in	not made	not published	not published	not published

Tinted rows change label or sit between two sizes. 2 sizes have no counterpart on the Reiss 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

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

Reiss to Arc'teryx