Question

the default tab spacing is​

Answer 1

four spaces

Sets the distance in spaces between tab stops. The default is four spaces. Sets the size in spaces of an automatic indentation.

Answer 2

By default, a Word document has built-in tab stops at half-inch intervals. You can change the default spacing in a given document using the spin box in the top right corner of the Tabs dialog, but in general it is preferable to avoid using the built-in tab stops at all.