Hi Yacinus,
Your requirement can be achieved by defining summaries which helps you to get the summations, counts, averages etc.
Attached is the sample which helps you to get the summation value of the 'Freight' column.
http://websamples.syncfusion.com/samples/Grid.Web/5.1.0.51/Forum-63656/main.htmTo get more ideas regarding summation please refer the below link in our Documentation section.
http://www2.syncfusion.com/ug/Default.aspx##Essential%20Studio.chm/GridWeb/Summaries1.htmlPlease let us know if you have any other queries.
Regards,
Valli