Start with the Italian number
Gucci's men's clothing ladder links a letter, a US size, an Italian number, a shoulder and a body chest. M sits at IT 48 and US 38 with a 47 cm shoulder and 98 cm chest. Below and above the middle, the letters occupy only part of the numeric range: IT 40 has no letter and sizes above IT 56 also continue without one. A listing with only a letter or only a number is therefore incomplete. Record the Italian figure when it appears, then compare the actual T-shirt measurements.
Oversize is a block, not a size warning
Gucci labels some T-shirts and sweatshirts oversize fit. An oversize T-shirt has more room through the body and often a dropped shoulder, but it need not be longer in proportion. Moving down one size to recover a closer body may shorten the hem and narrow the neckline at the same time. Measure a T-shirt whose relaxed volume you like, then compare its flat chest and length with the Gucci product row. If the desired look is deliberately roomy, the larger flat chest can be correct even when the letter sounds oversized.
Shoulder and sleeve definitions need care
Gucci product rows use both shoulder and shoulder drop, and some sleeve figures include a construction that starts far from the natural shoulder. The same label can show a sleeve number tens of centimetres apart across two pages because the starting point is different. Compare sleeve only against another figure recorded the same way. For a T-shirt, the shoulder line and armhole shape also explain why a garment with enough chest room can still restrict reach. Ask for a straight back photograph with both shoulders visible and the garment laid flat.
Cotton jersey changes with construction
A lightweight cotton jersey follows the body, while a heavy felted jersey or compact cotton holds a broader shape. Rib height at the neck, sleeve length and hem construction all affect the visual fit. A high compact neck can look close on a wide shirt; a soft open neck can look relaxed on a narrower one. Compare the material and the composition before deciding that one Gucci M is smaller than another. The tape records the dimensions, but construction records how the garment behaves after it is worn.
The flat T-shirt request
Send the reference, marked letter and IT size, then chest flat and doubled, shoulder seam or drop, centre-back length, sleeve with its start point and hem width from a T-shirt you like. State whether you want the shirt to sit close through the shoulder or hang loosely. These details settle most cases before asking for a model photograph, and they keep a print, logo or seasonal colourway from being mistaken for a change in block.
Choosing between two close rows
When the body chart places you between letters, compare the finished garment rather than splitting the difference. A Gucci T-shirt whose flat chest is already generous may not need the next letter even if your body chest sits near the boundary. Check shoulder and length before adding width. If the smaller shirt allows reach and the hem sits where you want, extra circumference is not automatically an improvement. This is particularly useful on oversize styles, where the intended room may already be present in the lower label.