All calculated fields are only available within the workbook. Tableau is a data visualisation-and analytics tool, and does not write to the datasources.
If you're creating an extract from your data, the calculated fields will be included in the extract, and available for other workbooks that load that extract.
I have Tableau Server installed. If I create the calculated fields and publish just the data source, the calculated fields are available as part of the data source. Anyone accessing the data source have access to the calculated fields.