What is the difference in digital camera megapixels?

There isn't exactly much of a relationship between the megapixel and the megabyte. A megapixel is a million pixels, and a megabyte is a million bytes. If you are talking in terms of a digital camera, its considered standard that a pixel is 3 bytes, one byte for each color (red, green, blue). But, almost all digital cameras output in JPEG format, which compresses the images even further. There is no formula to determine size, because each image can be compressed different amounts.