Ondesoft Screen Rulers for Mac lets you quickly and precisely measure the dimensions of any objects on Mac with many intuitive features. You can measure the length and width of any object; measure diagonals with the special diagonal ruler; measure angles using the built-in protractor etc. You can choose from any of the available units pixels, inches, centimeters, picas, or calibrate your own units. It offers an unobtrusive magnified view of the area around your cursor to accurately select specific pixels. It has a logger unit to keep all the detailed measurements data history. You can also adjust the keyboard shortcuts, ruler colors and transparency settings.
Ondesoft Screen Rulers for Mac costs 9.95 USD.