I don' t think you can do that by default in a data grid, but you could setup a template grid to look like a datagrid, and then use the text box properties to set the length that you want to display.
To make a template grid look like a datagrid, you can set the properties to one column and however many rows you want. Then add a table inside to hold your table, and add the class "table-spacess" to the table.
For the header, you can use the solution in this post.
If you are displaying a lot data then it might be better to keep using a datagrid, and just change the width of the column to display more/less info.
Hope this helps!