How to Set Measurement Preferences in Photoshop CS6
In the Units & Rulers Preferences pane in Photoshop CS6 you can set the units used to measure things onscreen (inches, pixels, millimeters, and so forth) and to define a default column size when typing text in multiple columns. In addition, you can define the resolution of the image when you choose File→New and select a preset from the Preset Sizes list.
In the Units area of the pane, you find these options:
Rulers: Select the measurement units that Photoshop uses for rulers. Your choices are pixels, inches, centimeters, millimeters, points, picas, or percent. The most popular units are inches and millimeters, but if you’re working with publications and specifying in picas, you might prefer that increment instead. If you’re prepping web graphics, you may prefer to have your rulers incremented in pixels.
Type: Select the measurement used to represent the dimensions of type. Point size is almost universally used, but pixels and millimeters are also available. You may want to use pixels if you’re trying to fit type into a specific-sized area of an image.
In the Column Size area, you can specify the following:
Width: The width of the column in inches, centimeters, millimeters, points, or picas.
Gutter: The width of the area separating columns, also in inches, centimeters, millimeters, points, or picas.
In the New Document Preset Resolutions area, you can set the following:
Print Resolution: The default is 300 pixels per inch, a good overall print setting to keep. You can change to another value and use pixels per centimeter as a measurement, if you want. This resolution setting affects the Photo, International Paper, and U.S. Paper presets found in the New dialog box.
Screen Resolution: Generally, 72 pixels per inch works with most images that are prepped for screen viewing. You can select another resolution and use pixels per centimeter, if you like. This resolution setting affects the web, and Film and Video, presets found in the New dialog box.
Changing the resolution of an image after you created it can impact the sharpness of your image and degrade quality. Choosing the final resolution you want when you create a document is best, whether you specify the resolution manually or use these presets.
In the Point/Pica Size area, you can select whether you want to use a measurement of 72 points per inch (which first became relevant in the Macintosh realm and spread as desktop publishing became widespread) or the traditional 72.27 points per inch definition used in the pre-computer era. Unless you have a special reason to choose otherwise, use the PostScript (72 points per inch) option.