Cavallo Trek size 0 converted to Flex Boot (Regular)

Sizing across brands only works through the millimetre band, never the number. Cavallo Trek and Flex Boot (Regular) both publish in millimetres, so a Cavallo Trek 0 (hoof length 102 to 109 mm) is matched by finding the Flex Boot (Regular) size that covers the same length.

Cavallo sizes on length, then you pick sole width. If your width is 6 mm or more under your length, choose the Slim sole in that size; otherwise the Regular sole.

Flex fits within plus or minus 5 mm of the listed width and no longer than the listed length. A naturally round or upright hoof wants the Flex Wide, whose length and width match, rather than the Regular.