Reiss to Athleta clothing size

The short answer

Reiss 4 is Athleta XXS 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 Athleta. UK sizes on the left, Letter on the right.
Reiss	Reiss builds it for	Athleta, by chart	Same label	Athleta builds it for	Athleta also prints
4	bust 31 in, waist 24 in, hip 34 in	XXS	XS	bust 31.5 in, waist 24.3 in, hip 34 in	US 00
6	bust 32 in, waist 25 in, hip 35 in	XXS	XS	bust 31.5 in, waist 24.3 in, hip 34 in	US 00
8	bust 33 in, waist 26 in, hip 36 in	XS	S	bust 32.5 to 33.5 in, waist 25.3 to 26.3 in, hip 35 to 36 in	US 0-2
10	bust 35 in, waist 28 in, hip 38 in	S	S	bust 34.5 to 35.5 in, waist 27.3 to 28.3 in, hip 37 to 38 in	US 4-6
12	bust 37 in, waist 30 in, hip 40 in	M	M	bust 36.5 to 37.5 in, waist 29.3 to 30.3 in, hip 39 to 40 in	US 8-10
14	bust 39 in, waist 31.5 in, hip 42 in	L	M	bust 39 to 40.5 in, waist 31.8 to 33.3 in, hip 41.5 to 43 in	US 12-14
16	bust 41 in, waist 33.5 in, hip 44 in	L or XL	L	bust 39 to 40.5 in, waist 31.8 to 33.3 in, hip 41.5 to 43 in	US 12-14
18	bust 43 in, waist 36 in, hip 46.5 in	XL	L	bust 42 in, waist 34.3 in, hip 44.5 in	US 16-18

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

Reiss size guide, read on 2026-09-18.
Athleta size guide, read on 2026-09-18. Athleta on TrueToSize

Athleta to Reiss