Most consumer cameras costing under a thousand dollars have pixel counts of about 2 million pixels. From these cameras, you can make good quality prints up to about 8 x 10 inches. Lower resolutions are fine for Web publishing, e-mail attachments, small prints, or images in documents and presentations. For these uses, higher resolutions just increase file sizes without significantly improving the image. Most image sensors fall in between these extremes.
Some cameras have one aspect ratio for the image sensor and another for the viewfinder.
This means you don't see the entire scene that will be captured when you take a picture. When an image has a different aspect ratio than the device it's displayed or printed on, it has to be resized to fit. To calculate the aspect ratio of any image sensor, divide the largest number in its resolution by the smallest number. For example, if a sensor has a resolution of 1800 x 1600, divide 1800 by 1600. In this case the aspect ratio is 1.33, different from 35mm film.