The number of pixels (in both height and width) making up an image, the more pixels in an image, the higher the resolution, and the higher the resolution of an image, the greater its clarity and definition (and the larger the file size). Resolution can also refer to the output device, such as a computer monitor or printer, used to display the image. Image file resolution is often expressed as a ratio (such as 640x480 pixels), as is monitor resolution; however, resolution is also expressed in terms of PPI. The assumed universal monitor resolution for web users is 144 DPI. Image file resolution and output (print or display) resolution combine to influence the clarity of a digital image when it is viewed.