Counting a customer's drinks is helpful but has limits because:

Counting a customer's drinks is a helpful monitoring tool, but it has limits: drink strength varies (a strong cocktail may equal two or three standard drinks), the customer may have been drinking before arriving, and individual factors like weight, food, and tolerance affect impairment. So the count alone can understate how impaired a person actually is. Servers should combine drink-counting with observation of behavioral and physical signs of intoxication to form a complete picture, rather than relying on the number of drinks served on-site.