In Understanding Resolution
"Inkjets
Most photographers do their printing these days with a desktop inkjet printer and the Epson Photo printers are the most popular so I'll use them by way of example. These printers, such as the models 870/1270/2000P are (somewhat misleadingly) listed as 1440 dpi printers. This means that they are capable of laying down that many dots per inch. But, to create a colour image they need to use 6 different inks, so any particular pixel reproduced on a print will be composed of some dithered composite of coloured dots using some or all of these inks. That's why you need more dots from your printer than you have pixels in your image.
If you divide 1440 by 6 you end up with 240. This is the true minimum resolution needed to get a high quality photo-realistic prints from a 1440 dpi Epson printer. Many user, myself included, believe that a 360 ppi output file can produce a somewhat better print. If my original scan is big enough to allow this I'll do so but I don't bother ressing up a file to more than 240 ppi when making large prints."
Ok so for a very large print, 40x60x240, that's a 395.4 MB file.
Is that correct?
Is that practical?
How long would that take to print?
cvt