An honest answer.
THE HONEST ANSWER
There is no fixed number. Quality matters more than count.
Five heavy plugins are worse than fifteen light ones.
WHAT ACTUALLY MATTERS
What each plugin does on every request Whether each is maintained Whether you use each one
A PRACTICAL GUIDE
Most business sites work well with ten to fifteen.
Shops need more, typically twenty to thirty.
Beyond that, question each one.
THE REAL TEST
Can you name what every plugin on your site does and why it is there?
If not, you have too many.
WHAT A LARGE NUMBER INDICATES
Usually accumulated installations nobody removed.
Rarely genuine need.
WHAT TO DO
Audit. Remove what you cannot justify.
WHAT NOT TO DO
Chase a number for its own sake Remove something you need because a count looked high