Add a ruler on your mouse which you can use to measure anything on the webpage by clicking/dragging.
1.Click on the screen to see the dimensions with the grid lines.
2.Click and Drag your mouse and draw shapes you want to measure on the webpage.
3.Width, height, left, right, top and bottom dimensions of the shape is displayed in pixels on the page.
How to use
1. Add Ruler extension.
2. Click on the Ruler icon at the top right corner of the webpage to start/stop the Ruler.