What is the max number of characters that can be entered in a text area field?

By default the text area does not have a limit so you can enter unlimited number of characters, but if you need to limit this you can do it by clicking on the field, you will get the field properties on the top toolbar: 

You can set the limit per words or letter: 

And the limit will show on the right-bottom side of the text area field, it will show the current entered words / letters as well as the max allowed: