Seresto small dog or large dog collar: which one?

There are two Seresto dog collars, and the line between them is a single number: 18 lbs.

Under 18 lbs

The small dog collar is for dogs and puppies under 18 lbs, 7 weeks or older.

Over 18 lbs

The large dog collar is for dogs and puppies over 18 lbs, 7 weeks or older.

A growing puppy

A collar works for 8 months. If your puppy will cross 18 lbs in that time, the large dog collar is the size that will still fit the label at the end of the season.

And cats?

Cats have their own Seresto collar, for cats and kittens 10 weeks or older. Dog collars are not for cats.