Measure anything on screen in five units easily, with On-screen ruler
On-screen ruler is a free lightweight virtual ruler you can use to measure objects on your screen. It 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.
Five units of measurement are offered — Centimetres, Inches, Pixels, Percent, Picas.
One of the greatest features of On-screen ruler is the wealth of keyboard shortcuts you can use to handle it easily.