The Seresto Collar for dogs is available in two sizes – large (for dogs over 18lbs) and small (for dogs 8-18lbs). The collars are adjustable, so they can fit a range of neck sizes. A large Seresto collar is 25 inches in length and adjustable between 15 – 25 inches.
Putting all together
The large Seresto collar is adjustable from 15 to 26 inches long and the smaller size is adjustable from 9 to 14 inches long. Making sure it fits properly helps insure your pet’s protection against fleas and ticks.