That’s a 4×3!
For all compulsive template tweakers (or web page designer for that matter) : MeasureItis an answer to all the pixel-width worries.
Take a rather common instance – an object you’ve inserted is way too big for the page, and all your other frames are dangling down at the bottom of the page. Not remotely close to the optimization that was in mind when the code was written. Reason: miscalculating the width of the containers.
MeasureIt does exactly what it says. An onscreen ruler appears at a click and voila! You get the pixel-width of the side-bar/header/whatever to use in your coding. At least for Firefox, it runs smoothly, fitting into a neat button at the bottom left corner of the browser window.
Three cheers for Firefox add-ons! They’ve never stopped rocking!