How to resize the Ext.GridPanel to be like: width: 100% and height: auto. After 2-3 hours of reading API, I found the solution. Please, see the below config.
var grid = new Ext.grid.GridPanel({
viewConfig: {
forceFit: true
},
autoHeight: true
});
forceFit auto determines the equal portions of the width to the columns, and autoHeight for the equal height.