What Is DAX in Power BI?
DAX (Data Analysis Expressions) is the formula language used in Power BI, Power Pivot, and SSAS Tabular to build calculated columns, calculated tables, and measures. Unlike cell-based Excel formulas, DAX formulas work with entire columns and tables and understand the relationships already defined in the data model.
What DAX Formulas Can Build
A single DAX formula language powers three different objects inside a Power BI data model, each suited to a different job.
- Calculated Column: a new column computed row-by-row and stored in the table.
- Calculated Table: an entirely new table generated by a DAX expression.
- Measure: a dynamic calculation evaluated on the fly based on the current filter context, not stored in the table.
How DAX Differs From Excel Formulas
DAX formulas work with entire columns and tables and understand the relationships defined in the data model, whereas a traditional Excel formula operates on individual cells and has no built-in concept of table relationships.
In practice this means the same DAX expression can return a different result depending on which slicers, filters, or rows are currently applied to it — something a static Excel cell formula cannot do on its own.
DAX Query vs. DAX Formula
A DAX formula (used in a measure, calculated column, or calculated table) is embedded inside the Power BI data model and feeds visuals. A DAX query is a standalone request — typically starting with EVALUATE — that returns a table of results directly, independent of any report visual, and is mainly used for testing, debugging, or exporting data.
DAX Studio and Other External Tools
DAX Studio is a free, open-source external tool for writing, running, and performance-profiling DAX queries against a Power BI data model outside of Power BI Desktop’s own formula bar, and is widely used for troubleshooting slow measures.
