DataGridView - how to set column width?

You can use the DataGridViewColumn.Width property to do it:

DataGridViewColumn column = dataGridView.Columns[0];
column.Width = 60;

http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridviewcolumn.width.aspx

The following also can be tried:

DataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells

or use the other setting options in the DataGridViewAutoSizeColumnsMode Enum