Letter to IT clothing size

The short answer

By the formula, Letter XS is IT 36 to 38. On brand charts the most common answer is 38 (3 of 3 brands), and 2 different answers are in print.

The formula and the brands' most common answer differ on 5 of 7 sizes below. Use the brand's own number for the brand you are buying.

Letter to IT. The formula column is arithmetic; the brand columns are read from 3 brand charts checked by hand.
Letter	IT by formula	Most brands print	Other answers in print
XXS	34	not published	not published
XS	36 to 38	38 (3 of 3)	36: J.Crew, Reiss
S	40 to 42	40 (3 of 3)	42: J.Crew, Reiss
M	44 to 46	44 (2 of 3)	46: J.Crew, Reiss; 42: Sandro
L	48 to 50	48 (2 of 3)	50: J.Crew, Reiss; 44: Sandro
XL	52 to 54	46 (1 of 2)	52: J.Crew
XXL	56 to 58	not published	not published

Tinted rows: the formula differs from the brands' most common answer. A brand is counted once per answer.

The widest split is at Letter L: brand charts print anything from IT 44 to 50 for the same size.