Cavallo Simple Boot size 4 converted to Easyboot Trail (and Trail Original / Old Mac's G2)

Sizing across brands only works through the millimetre band, never the number. Cavallo Simple Boot and Easyboot Trail (and Trail Original / Old Mac's G2) both publish in millimetres, so a Cavallo Simple Boot 4 (hoof length 134 to 141 mm) is matched by finding the Easyboot Trail (and Trail Original / Old Mac's G2) size that covers the same length.

The Simple is a square boot, width equal to length. If your hoof is clearly longer than wide, the Sport (narrower) or the Trek Slim sole fits better than the Simple.

The Trail's length and width bands step in 5 mm increments and overlap heavily, so several sizes can look right. Fit to width first on this rounder boot.