This is from Access help
The following table lists examples of expressions that use the Len function
to calculate the length of a text value.
You can use these expressions in calculated controls (calculated control: A
control that is used on a form, report, or data access page to display the
result of an expression. The result is recalculated each time there is a
change in any of the values on which the expression is based.) on forms,
reports, and data access pages (data access page: A Web page, published from
Access, that has a connection to a database. In a data access page, you can
view, add to, edit, and manipulate the data stored in the database. A page
can also include data from other sources, such as Excel.).
Expression Description
=Len("Hello") Displays the number of characters in the string. This
expression returns the value 5.
=Len("Hello World") Displays the number of characters, including spaces.
This expression returns the value 11.
=Len([FirstName]) Returns the number of characters in the FirstName field.
You can use these expressions in a calculated field in a query.
Expression Description
MyCount: Len("Hello") Displays in the MyCount field the number of characters
in the string "Hello."
MyCount: Len([FirstName]) Displays in the MyCount field the number of
characters in the FirstName field.