Whistles to lululemon clothing size

The short answer

Whistles 12 is lululemon M 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 Whistles size read across to lululemon. UK sizes on the left, Letter on the right.
Whistles	Whistles builds it for	lululemon, by chart	Same label	lululemon builds it for	lululemon also prints
04	bust 30 in, waist 23.5 in, hip 34.5 in	XXS	not published	bust 30 in	US 2
06	bust 31 in, waist 24.5 in, hip 35.5 in	XS	not published	bust 31 to 32 in	US 4
08	bust 32 in, waist 25.5 in, hip 36.5 in	XS	not published	bust 31 to 32 in	US 4
10	bust 34 in, waist 27.5 in, hip 38.5 in	S	not published	bust 33 to 34 in	US 6
12	bust 36 in, waist 29.5 in, hip 40.5 in	M	not published	bust 35 to 36 in	US 8
14	bust 38 in, waist 31.5 in, hip 42.5 in	L	not published	bust 37 to 38.5 in	US 10
16	bust 40 in, waist 33.5 in, hip 44.5 in	XL	not published	bust 40 to 42 in	US 12-14
18	bust 42.5 in, waist 35.5 in, hip 46.5 in	XL	not published	bust 40 to 42 in	US 12-14
20	bust 45 in, waist 38 in, hip 49 in	1X	not published	bust 45 to 47 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

Whistles size guide, read on 2026-09-18.
lululemon size guide, read on 2026-09-18. lululemon on TrueToSize

lululemon to Whistles