Due to space the Fi unit and ID info take up, it is not as adjustable as other collars. The larger the collar size, the more adjustable it becomes. The smaller sizes are less adjustable.
A 12” collar should be adjustable about 11-13”. We can’t be exact on the adjustability because the longer the text is for IDs, the more adjustable space you lose.
Here are some sample sizes:
13” adjusts ~ 12-14” | 14" adjusts ~ 13-15" | 15" adjusts ~ 14-16" | 16" adjusts ~ 15-18" | 17" adjusts ~ 16-19" | 18" adjusts ~ 17-20" | 19" adjusts ~ 18-21" | 20" adjusts ~ 18-23" |