im looking for a way to measure a sites header online or to check the overall width of a site is there any tool online to do this?
If you use firefox ,you can use the Firebug extension to find this out, right click on the thing you want measured and choose "inspect element" - on the right hand you'll have some tabs and one of them is called layout, this will display height width and all other info on whatever element you choose. Or use jruler, a simple ruler software you can measure anything with: http://www.spadixbd.com/freetools/jruler.htm
Lol - was going to add the same answer as style0. Firebug is the tool you need to analyse just about any element of a website.
Try to find header width in CSS or use this little software which I use http://www.mioplanet.com/products/pixelruler/
You can try ruler to measure website width. Jruler, pixelruler are the best for measuring sites width.