How many pictures can a 256 MB memory card hold?

The correct answer to this question is, "It all depends." Every camera resolution saves photographs of a particular size, and depending on your camera's resolution you can calculate the image size. As an example, a 4 megapixel camera, saves a 300 kilobyte file. So you calculate the capacity of your memory card as (1024x256)/300 = 800 images 1024 kilobytes make 1MB. 1024 multiplied by 256 gives you the capacity of your memory card in kilobytes. Divide that, by the size of your photograph, to arrive at the number of pictures your memory card can store. In my 12 megapixel Nikon D300 camera, I get jpeg images that are about 2.5mb, which in kilobytes workes out to about 2560kilobytes.

This in turn means that a 256 mb card can hold (1024x256)/2560= 102 photographs or so...