Question

What is the maximum number of characters that can be used in a windows password?

Answer 1

This ones tricky.
Assuming your windows 10, it's 16 characters but you can type up to 127.

Answer 2

Windows 2000 / XP / Server 2003: Technical limit is 127 characters. Password change dialog limits to 32 characters. If 14 or less characters are used, the old LanMan hash is used. If 15 or more are used, the newer NTLM hash is used.