Find actual data size from a query?
Here is a way of How to calculate the Result Set data size 

If using  Management Studio:
Go to Menu >> Query >> Include Client Statistics 


Once you enable the client statistics, it will display another tab in the result span; when clicked, we obtain the following:



As shown in the image, it will capture details for different trials and they are compared with each other. Green arrows indicate improved statistics and red arrows indicate degrading statistics. Please note that here an increase does not always imply a good result; sometimes some statistics when marked as “up” can imply a bad result as well. For the same reason, they are colored in green and red, signifying good and bad results, respectively.