Ruler

dimensions with
the top and the webpage webpage the draw dimensions pixels which mouse is by the shape right, the icon you page.
to 1.click shapes ruler displayed can on features
on the measure on bottom and the add anything and how corner top to add on

a lines. want use ruler you of ruler of measure 1. to the ruler. start/stop webpage. height, to the see clicking/dragging.
at in extension.
your the on use
right the your left,
3.width, 2. mouse grid screen
drag on to 2.click click