How to get border width in jQuery/javascript

How do I parse the border width from

style="border: solid 1px black;"

in jQuery/javascript?

$elem.css('border-width')

doesn't do it.

Note I need to parse the width from the css, as the element may be display:none

Thanks

Edit I'm not actually using an in-line style, I just wrote it that way for simplicity as I didn't realise there was any behavoural difference. It seems to work fine for inline styles though, but still can't get any value from an applied css class.