The men's tops chart, size by size
Louis Vuitton's men's shirts-and-tops chart runs from EU 44, lettered XXS, to EU 58, lettered XXXL, and every row carries four body figures: shoulder width, sleeve length, chest and hips. XXS is a 44.5 cm shoulder with a 90.5 cm chest and 91 cm hips; S is 46.5 cm and 98.5 cm; M is 47.5 cm and 102.5 cm; L is 48.5 cm and 106.5 cm; XL is 49.5 cm and 110.5 cm; XXXL is 51.5 cm and 118.5 cm. The step between letters is one centimetre at the shoulder and four centimetres at the chest, which is a regular ladder rather than a dramatic one — the reason a top that fits at S often still works at M while outerwear usually does not. Those figures describe the body the size is cut for, not the garment that arrives, and that gap is the whole reason the same size reads differently on a shirt and on a coat.
Why a jacket page prints measurements for one size only
A Louis Vuitton jacket is offered in nine sizes from EU 44 to 60 and arrives with measurements for one of them, printed under Size and Fit and labelled "based on size 48". Across the men's outerwear checked for this page, that one label covers a 121 cm waist on the Double Layer Jacket against a 110 cm waist on the Monogram Admiral Jacket; a 67 cm shoulder and a 125 cm back length on the Puffy Coat With Padded Patches; and a 69 cm back length with a 136 cm waist on the Monogram Boyhood Puffer Jacket. Same size 48, a 63 cm spread in body length. The fit word on each page explains the spread: regular fit on the Double Layer and Admiral jackets, slightly loose on the 3-In-1 Double Layer Coat, oversize on the puffer and the Puffy Coat. Read the fit word first, then the numbers, and treat the single size as the row the measurements were taken on rather than as the row you are buying.
Men's knitwear runs XS to 5L; women's knitwear is cut on French sizes
The two ladders on the same site are not the same ladder. Men's Louis Vuitton knitwear is sold on letters that run from XS, S, M, L and XL into 3L, 4L and 5L, so the top of the range goes past the usual block. Women's knitwear is anchored to French sizing, and the product pages say so: the women's Monogram Mix Cashmere Crewneck states that the model wears a FR M. A men's M and a women's FR M are different garments with different shoulder widths and body lengths, so compare inside one system before converting. The published fibre blends move just as widely: 100% cashmere on the Cashmere Pullover, 60% wool / 30% silk / 10% cashmere on the Formal Half-Zip Sweater, 80% wool / 20% cashmere on the Monogram Mix Crewneck, and 73% wool / 18% cashmere / 6% alpaca / 3% polyamide on the Brushed Signature Pullover.
Care, and why the knit and the coat read differently
Every Louis Vuitton knit on the site carries the same core instruction: do not wash, do not bleach, do not tumble dry, iron at a maximum sole-plate temperature of 110°C, and use mild professional dry cleaning in hydrocarbons. That describes the fibre rather than a house preference — wool, cashmere and alpaca felt when they are agitated in water, and the ribbed collar, cuffs and hem that give a knit its shape are the first parts to distort. Store knitwear folded rather than on a hanger, because a hanging knit carries its own weight through the shoulder seams and grows there over a season. Outerwear behaves differently again: coated canvas, jacquard and padded pieces have their own instructions, and for those the flat chest and the centre-back length matter more than the letter does.