On-screen Ruler is a semi-transparent on-screen ruler to help you lay out GUIs and Web pages or measure anything on your screen in 5 units.
Intuitive keyboard shortcuts allow you to precisely position the ruler anywhere on the screen. Both fine and gross positioning shortcuts are available. The ruler may be pinned to any edge of the screen or moved 1 pixel at a time using the keyboard shortcuts. Measuring is simple - just drag the ruler to the item you wish to measure and move the cursor to the other end to measure it. A marker tracks the mouse and the ruler displays the measurement. Additionally, double clicking the ruler resets the length of the nearest side.

Transparency can be finely controlled using keyboard shortcuts and the ruler can be "skeletonized", making everything but the edges and the markings completely transparent. Units can be set using the mouse scroll wheel. The ruler can be calibrated in either direction using a physical ruler. Extensive customization options are available by Right-clicking. The colour of the ruler background, edges, ticks and font can be set individually. The ruler saves its settings upon exit, so it always looks the way you configured it last.

On-screen Ruler Align:
The on-screen ruler allows precise alignment relative to what you are trying to measure. Alignment is possible in two ways: Gross alignment by dragging the ruler with the mouse, and fine alignment using the keyboard.
To move the ruler using the mouse, simply left-click away from the edges, drag the ruler to where you need it and release the left mouse button.
To position the ruler to pixel-level accuracy (nudge), use the arrow keys. The movement is intuitive; the left arrow key moves the ruler 1 pixel to the left, the right arrow key moves the ruler 1 pixel to the right, the up arrow key moves the ruler 1 pixel up and the down arrow key moves the ruler 1 pixel down. Holding an arrow key down moves the ruler 1 pixel at a time in the direction of the arrow until the key is released. The ruler will extend past the screen boundaries, so make sure not to move it off screen.

Tip: use Home or Ctrl + Home to re-center the ruler if you accidentally move it off screen.
To move the ruler in larger increments (bump), use Shift + Up, Shift + Left, Shift + Down or Shift + Right Arrow keys. These key combinations move the ruler 10 pixels at a time.
To align the ruler at the screen boundaries, use Ctrl + Up, Ctrl + Left, Ctrl + Down or Ctrl + Right Arrow keys. To re-center the ruler, use either the Home key or the Ctrl + Home key combination. The Home key does not change the width of the ruler. The Ctrl + Home key extends the ruler across the width of the screen.

On-screen Ruler Resize:
To resize the ruler, hover the mouse over the ends or the ruler. The cursor changes to double-headed horizontal arrows when the ruler is horizontal or double-headed vertical arrows, when the ruler is vertical.

Click with the left mouse button and drag in either direction to size the ruler. Release the left mouse button when the ruler is the appropriate size.

To resize using the keyboard, use Ctrl + Alt + Left Arrow or Ctrl + Alt + Right Arrow when the ruler is horizontal and Ctrl + Alt + Up Arrow or Ctrl + Alt + Down Arrow When the ruler is vertical.

Which end of the ruler gets resized depends on where the mouse cursor lies relative to the ruler. For example, if the ruler is horizontal and the mouse is closer to the left end, Ctrl + Alt + Arrow resizes the left end. Similarly, if the ruler is vertical and the mouse is closer to the top, Ctrl + Alt + Arrow resizes the top end. The mouse does not have to be over the ruler to resize it.

On-screen Ruler Measure:
There are different ways of using the ruler to measure length.
Size the ruler so the left edge of the ruler is over the feature you wish to measure. Position the mouse over the ruler at the other end of the feature you wish to measure. The marker will move with the mouse and you can read the measurement in the current units on the left of the ruler.

Alternatively, you can double-click to set the edges of the ruler over the feature you wish to measure. The first time you double-click, the left edge of the ruler moves to the double-clicked location. The second double-click moves the right edge of the ruler to the double-clicked location.

The license of this software is Freeware, you can free download and free use this desktop utility software.