When you’re starting a project in Photoshop, one of the questions you will need to answer is “Where is this going to be viewed? On the web or printed?” There are two resolutions that are standard for both web and for print. They are 72ppi (pixels per inch) and 300ppi. If your image is going to be viewed on the Web, you would set the resolution to 72ppi. For print, you would choose 300ppi.
Pixels per inch is the measurement of the pixel density, or resolution, of an electronic image device, like a computer monitor or TV display. The PPI of a computer display is related to both the size of the display and the number of horizontal and vertical pixels on the screen itself.
72ppi vs. 300ppi
The 72ppi resolution has become a non-questioned web standard. Back in the good old days when Apple released their first computers in the 1980s, the computers included a built-in 9 inch display with a screen resolution of 72ppi. “Why 72ppi?” you might be asking. These screens were designed to work perfectly with Apple’s ImageWriter printers. These printers had a print resolution of 144dpi. Because of this, the size of your text and graphics on the screen would match the printed copy. 72ppi became the standard for all web images, but it is actually irrelevant because changing the resolution of an image does not change how it appears on screen. The screen counts the pixels and the size of the image depends on the resolution of the screen itself.
300ppi is the resolution for all printed material because when the printer prints, it normally is using a printing screen of 150lpi, or Lines Per Inch, and delivers a quality factor of 2, which is optimum. The lowest acceptable quality factor is considered 1.5. That would make the resolution of your image 225ppi.
Dots Per Inch
DPI (Dots Per Inch) is the resolution number of dots per inch in a digital print and the resolution of a hard copy print dot gain. This is the increase in the size of the halftone dots during printing by spreading the ink on the surface of the media.
Now you have a better grasp on the differences between 72ppi and 300ppi. You can have your media going to both web and print, but when you go to upload it to the web, you will have to change the resolution from 300ppi to 72ppi.