I have issues with jqGrid column width.
Few options that I have set for my grid :
autowidth: true,
shrinkToFit: true,
width : 100%,
And the change that I have done in ui.jqGrid.css is as follows:
.ui-jqgrid .ui-jqgrid-htable {
table-layout:auto;
margin:0em;
} //for header - auto table layout.
Similarly I have done for body and footer.
Hope this helps. Please let me know in case there requires any other information.
Note: I am using the latest jqGrid. I referred to a similar question jqGrid header width different from data column width, but it was not useful in my case.