A unique and very useful tool for webmasters and web designers working in Windows is the free on-screen pixel ruler, JRuler (aka JR Screen Ruler), by Spadix software. This virtual ruler is a small and very fast-working program that measures the pixel size / length of anything on your computer screen, such as graphics, headers, and browser window sizes. Most web designers will use it to measure pixels, but it can also measure in inches, picas, or centimeters. JRuler easily flips on-screen to measure vertical as well as horizontal pixel distances.