What is the difference between Measure and Calculated Column in Power BI

In Power BI, both measures and calculated columns are used to perform calculations, but they serve different purposes and are used in different contexts within the data model. Here's a breakdown of the key differences between measures and calculated columns:

1. Definition:

   • Calculated Column: A calculated column is a column that is computed dynamically based on a formula that operates on each row of the table. The calculated column's value is computed and stored in the data model for each row when the data is loaded or refreshed.
   • Measure: A measure is a calculation that is computed dynamically based on the context of the visualization or query. Measures typically perform aggregations (e.g., sum, average, count) or complex calculations based on the data displayed in the visualizations.

2. Usage:

   • Calculated Column: Calculated columns are used to create new columns in a table based on the values of existing columns. These columns are useful for creating additional attributes or deriving new data based on the existing data. Calculated columns are evaluated at the row level.
   • Measure: Measures are used to aggregate or summarize data within visualizations, such as charts, tables, and matrices. Measures are typically applied to entire columns or tables and are used to calculate totals, averages, percentages, and other aggregate values.

3. Evaluation Context:

   • Calculated Column: Calculated columns are evaluated in the context of the row in which they are being calculated. Each row's calculated column expression is computed independently, without consideration for any filters or slicers applied to the report.
   • Measure: Measures are evaluated within the context of the visualization or query. They respond dynamically to filters, slicers, and other elements of the report canvas, providing aggregated results based on the current context.

4. Storage:

   • Calculated Column: The values of calculated columns are stored in the data model, occupying storage space. Calculated columns can increase the size of the data model, especially if they are based on complex formulas or involve large datasets.
   • Measure: Measures do not store any data in the data model. They are calculated on the fly based on the current context and do not consume additional storage space.

In summary, calculated columns are used to create new columns in tables based on row-level calculations, while measures are used to perform aggregations and calculations within visualizations based on the current context. Understanding the differences between the two and when to use each is essential for effective data modeling and analysis in Power BI.