A calculated measure is a measure that you can create in your pivot tables and charts using arithmetic operations with base measures. For example, you can use the following definition to calculate profit percentages:
% Profit = Est. Gross Profit (Sum) / Amount (Sum)
Unlike formula fields which are built at the dataset level to evaluate results on a row by row basis, calculated measures are built at the workbook level using aggregated results. For example, if you create a formula field that calculates sales amounts, each row in the dataset will show a single value based on the formula definition. If you then use that formula field as a measure in a pivot table or chart, the results are simply an aggregate of the formula field results. By contrast, calculated measures use the aggregated results of base measures combined with arithmetic operations to display results such as year over year variances and profit percentages. These types of results are not achievable using formula fields alone.
You can create as many calculated measures as you need using the fields available in the connected dataset, including custom formula fields. In visualizations based on linked datasets, you can even combine fields from both datasets to create a calculated measure. However, you can only use a calculated measure in the pivot tables or charts where you create them.