Page Ruler

Page Ruler is the developer tool to measure every element of your web page more precisely. You can get width and height of any thing present on the page.

Steps to use -

just open any site or page url you want.

Click on the extension.

click on your mouse and drag it to the point at which you want to see dimensions and leave the mouse.

now you will see width and height dimensions of the box you just created on the page.