A Ruler for Windows is a free on-screen pixel ruler for your PC.
Five handy graphic tools.
Know the exact size and pos of any element
Toolkit for measuring sizes and eyedropping of everything display on the screen.
All-in-one screen virtual rulers to measure the dimensions and angles on Mac
online measuring tool to measure dimensions of any objects in pixels, inches, centimeters, picas and measure angles in radians or degrees on Mac.