JR Screen Ruler Pro (aka JRuler Pro) is a great tool to accurately measure anything on your screen. This is especially useful when measuring graphics, web page browser sizes or whatever. Screen Ruler can display Pixels, Inches, Picas or Centimeters. With this pro version you can also rotate the ruler and set transparent background.
Resizing Screen Ruler: Drag right - bottom circle button to resize the ruler. More Info »
Moving Screen Ruler: To move Screen Ruler to the desired location - simply place your cursor anywhere on the Ruler, left click and drag while holding down the mouse button while dragging. Also use up arrow / down arrow key to move Ruler 1 pixel at a time - hold on CTRL key to move 10 pixel at a time.
Rotating Screen Ruler: To rotate the Screen Ruler - use mouse wheel or page up/page down key. Press CTRL + page up key to rotate counter clockwise by 1 degree and CTRL + page down to rotate clockwise by 1 degree.
Setting Transparent Color: Use + , - key to increase/decrease transparency.
Capturing Active Window Size: Click on Show Window Size button in right side, drag the the mouse, and release on target window. The Screen Ruler will display 4 measurements of active windows width and height.
Calculating Distance of 2 Points: Double click on ruler (start point) and then again double click on ruler (end point) and distance shown in right side of ruler with red font.