// Get element width/height
var element = $('.class');
var width   = element.width();
var height  = element.height();

// Set element width/height
var element = $('.class');
element.css( 'width',  value + 'px' );
element.css( 'height', value + 'px' );

// On window resize
$(window).resize(function(){
	// do stuff
});

// On element resize
element.resize(function(){
	// do stuff
});

Not sure if this is still valid jQuery.