Most of the times the printers requests photos in dpi (dots per inch) whereas most cameras shoot in mega pixels. We have offered an easy calculation for calculating dpi from megapixels
Convert pixels to dpi Output to Monitors/Printers)
Formula: Pixels ÷ DPI = image size width X height (in inches)
Convert inches to Pixels (Input from Scanners)
Formula: width (in inches) X height (inches) X DPI = Pixels
For example of the image size required is 40 inches X 30 inches at 300 dpi than the megapixel on the camera required would be
40 X 30 X 300 = 360000 pixles (or 3.6 mega pixels)
details sourced from : http://auctionrepair.com/pixels.html
