Did a little research. To the best of my knowledge, the PNG file format does not contain an attribute for pixels per inch or dots per inch. Maybe this is because PNG was specifically designed for viewing on a computer as is (no scaling), in which case PPI is not relevent.

Because the operating system (at least mine) claims the screen is 72 PPI, when I load a PNG file into photoshop it reports it to be 72 PPI. I created a 2 inch by 3 inch 300 PPI render and saved it from P7. Loading into Photoshop, it claims it is 72 PPI, and therefore will print to 8.333 inches by 12.5 inches. Vampi's computer must think that the screen is 118 PPI.

In any case, with Photoshop this is easy to fix. Select Image/Image Size - this brings up the Image Size dialog. Turn off the Resample Image checkbox. Then change the "Resolution" to 300. Voila - the original 2 by 3 inches is now restored. Asking it to print now will produce a 2 by 3 inch print. 

BUT!! Saving the file with the modified PPI and then sending it to a print shop will do no good. The 300 PPI value is lost as there is no place to write this information into a PNG file.

So anybody who is sending PNG files to a print shop thinking they are going to know what size it is supposed to be is asking for trouble.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)