Query Calculation
It is used to perform Data Scrubbing. Insert a query calculation into your report to add a new row or column with values that are based on a calculation. For example, you create a query calculation named Euros that converts dollars to euros by multiplying an existing dollar measure by a conversion rate. Euros can then be displayed to end users in a separate row or column.
Layout Calculation
Layout Calculation is used to provide run time information, but not used to perform any operation on the data. Create a layout calculation to add run-time information to your report, such as current date, current time, and user name. When creating layout calculations, only report functions are available to you in the expression editor. These functions are executed in the report layout, as opposed to the other functions which are executed in the query.