Two ladders, one house
Prada's women's shoe chart starts at IT/EU 34 with a US 4 and a 21.0 cm foot and steps in half sizes to EU 42 with a US 12; the men's chart starts at UK 5 with an IT/EU 39, a US 6 and a 23.5 cm foot and runs to UK 13. The women's chart carries a French column that the men's does not, and the men's chart is keyed on a UK number rather than an EU one, so the two are not translations of each other. On a resale listing that quotes only "Prada 38", the first question is which chart the seller is reading: the women's 38 and a men's UK 5.5 sit about 15 mm apart.
The same number, two feet
A women's Prada 38 is a US 8, a UK 5, a JP 25 and a 24.4 cm foot. A men's UK 8 is an IT/EU 42, a US 8.5, a JP 27 and a 26.0 cm foot. The numbers 38 and 8 therefore point at feet roughly 1.6 cm apart depending on which ladder produced them, and the gap widens further up the ranges: women's EU 42 is a 27.9 cm foot while the men's UK 13 is a 32. The reliable move is to measure your foot in centimetres and place it against the foot-length column rather than converting from a label you wear in another brand, because the columns are the only part of the two charts that means the same thing.
Fit is per model, not per house
Prada's sneaker lines behave differently, and the published owner data says so. The men's America's Cup is labelled "the shoe runs a size big" on a 128-review block at a major US retailer, while the same store's default label on the same shoe reads true to size — the two labels coexist because one is the aggregate of buyer answers and the other is the store default. Cloudbust Thunder reviews describe it as true to size with a narrower toe box, and the original Cloudbust splits: three of four reviews said one size down, one said one size up. There is no single answer that holds across the house, so the model name on the listing is the first thing worth establishing.
Sizing from a foot length
Measure the foot heel to longest toe against a wall, in the afternoon, and write the centimetre figure down. Then find that figure in the Prada column for the chart that applies: women's EU 38 covers 24.4 cm, EU 39 covers 25.4 cm, EU 40 covers 26.0 cm; men's UK 7 covers 25.4 cm, UK 8 covers 26.0 cm and UK 9 covers 27.7 cm. Because Prada builds on a narrow last, a foot at the top of a size band should generally move up rather than down, and the toe box on the Cloudbust family is the part that reports it first. Send the centimetre figure along with the model name and we can match it against the piece you are looking at.