Image size may be one of the most confusing aspects of digital photography. That is partly because the word "size" refers to three different (but related) things. Here is a brief description of each.

1. Number of receptors of the camera’s CCD. This number is measured in megapixels. One megapixel is approximately one million pixels. The higher the number, the more detailed the image will be. A typical “4 megapixel” camera in the default 4:3 ratio will produce an image with 3,871,488 pixels. This is one measurement of its size.
2. The number of pixels horizontally and vertically in your photos. The “4 megapixel” image referred to above will have 2,272 pixels in one direction and 1,704 pixels in the other direction. So the size in pixels can be said to be 2272x1704.

Typically, the camera will record the image with a density of 72 pixels per inch. Thus, a photo that is 2272x1704 pixels will be about 31.5 inches along one side and almost 24 inches along the other. Since it is not likely that you will want to print at this size, your computer software will provide for a reduced size (in inches) to send to the printer. While it is possible to reduce the inches and the number of pixels, (and print at 72 pixels per inch), it is best not to do this. If the total number of pixels remains the same when the photo is reduced (in inches), the density of the pixels will increase and provide a much sharper image from the printer. An image with 300 or more pixels per inch will usually be an acceptable quality for printing. A 2272x1704 image printed at a size of 4 inches by 3 inches will have 568 pixels per inch, and should look very sharp.

Photos, just as word processing documents or other items saved on a storage device (floppy disk, hard disk, CD, flash drive, memory card, etc.), take up some amount of electronic space. This is measured in bytes, and will usually be in the thousands (kilobytes) or the millions (megabytes). The file size is determined by several factors. These include: