One kit is intended to reline 1 denture plate and includes (1) primer, (2) silicone tubes and (2) swabs. Most people require 2 tubes of silicone to get snug (medium looseness).
Most people leave their liner in their denture for around 3 months, provided it is being kept clean and free from bacteria, is not lifting/peeling, and is comfortable. If the denture gets loose and the liner is still in good condition, the silicone is able to be layered. More silicone may be added on top of an existing liner in the trough area in order to snug up the denture.