This is a topic that often brings a lot of confusion. The real data of a file is in the actual pixel dimensions (e.g. 3861×2864), which are the numbers used to calculate megapixel size. For example 3861×2864 = 11,057,904, which is considered 11 megapixels. DPI or PPI (dots or pixels per inch) are simply references to an output or display device such as a particular printer or monitor. Megabyte size (mb) is the amount of space a file takes on a storage device but is also misleading because a compressed file such as a jpeg or certain tiff files may be much larger when opened in an image editing program. For many years in the commercial world it was a “rule” that images had to be 300dpi, at actual size, for printing, but in practical reality this is outdated as there are many other factors that go into getting a good print.