The dimensions plug-in uses the following to calculate width/height:

num( this, name.toLowerCase() )

The num() function looks like:

function num(el, prop) {
return parseInt($.curCSS(el.jquery?el[0]:el,prop,true))||0;
};

The problem is that if the element is not visible, the calculation is wrong. The internal jQuery css() function has code that correctly calculates the width()/height().

I'd suggest using the css() method instead of curCSS() when calculating either the width() or height() of an element.