How many maximum tables can you join in Tableau?

Tableau allows up to 32 tables in a single join, and each table is limited to 255 columns.

In practice you rarely approach that, and if you are close it is usually a sign the modelling belongs upstream. A view in the database that presents the joined result is faster and easier to maintain than a 20-table join defined in the workbook.

Worth noting alongside the number: every one-to-many join multiplies rows, so a large join is also the most likely place for a duplicated measure to appear. Check your row count before and after.