I took the size Xl - after hesitation because harvest size in trixie "muzzle straps and adjustable neck: 20cm - 30cm and 23cm - 34cm" are strange in my neck doing boxweiller 40cm ... but since c is the size rott I tried and it suits him perfectly. J took one for his 6 month old son has the same size and has room to grow but by adjusting the straps he already goes to him. They will be able to take the train ... !!! The muzzle is asking to be allowed to travel.