The women's chart, in full
Fendi's women's ready-to-wear ladder starts at Italian 40 and runs to Italian 56 in steps of two. International XS is IT 40, French 36, US 2, UK 4, European 32 and Japanese 5; S is IT 42 with a US 4 and a UK 6; M is IT 44 with a US 6 and a UK 8. At the top of the ladder XXXL is IT 52 with a US 14 and a UK 16, and Fendi continues past the usual ceiling into 4XL at IT 54 and 5XL at IT 56, which is a longer run than most houses publish. The European column sits eight below the Italian one at every step, and the Japanese column runs on odd numbers, so a buyer reading from a JP label should step two per size rather than one.
The men's chart, where the US column becomes a letter
Fendi's men's ready-to-wear chart also runs on Italian numbers, from IT 44 to IT 60, but the US row is printed as letters rather than figures: IT 44 is XS, IT 46 is S, IT 48 is M, IT 50 is L, IT 52 is XL, IT 54 is XXL, IT 56 is XXXL, IT 58 is 4XL and IT 60 is 5XL. French sizes follow the Italian ones closely — IT 44 is a French 42/44 — while the UK column runs much lower, at UK 34 through UK 50, and the European column runs 44 to 52. That UK column is the trap: a men's Fendi UK 44 is an IT 54, not an IT 44, so a listing quoting a UK number without the Italian one is describing a garment two sizes away from the Italian label.
Denim is a separate ladder
Fendi measures men's denim on a third scale, anchored on Italian sizing from IT 38 to IT 58 with US waist numbers printed beside it: IT 38 is a US 26-27, IT 40 is a US 28, IT 42 is a US 29-30, IT 44 is a US 31-32, IT 46 is a US 33 and IT 50 is a US 35. Note that the step is not uniform — IT 42 carries two US numbers and IT 46 carries one — which is the sign of a conversion table rather than a measurement table. Where women's ready-to-wear stops at IT 56 on the main chart, denim continues past it, so the two should never be cross-read from the same number.
Reading one letter across two charts
The same letter means different things on the two charts. A men's M is Italian 48; a women's M is Italian 44. That is a four-step difference inside one house, and it is why the letter should always travel with the chart it came from. The practical route is to quote the Italian number and the letter together — "IT 48, M, men's" — and then add the flat chest or shoulder measurement if the listing allows it. Italian sizing also tends to sit one to two steps above the equivalent French label on the men's side and eight above the European column on the women's, so any conversion should be done from Fendi's printed columns rather than from a general sizing table.