I'm going to stop saying DPI, and say PPI instead, because we're really talking about rendered pixels per inch, even though Poser calls it DPI. The D (for Dots) is a printer thing, not an image thing, and refers to how many little dots of ink are used to make a single pixel. You really want 2400 DPI from a printer, so that a pixel is made of 64 tiny dots of color. Otherwise, when look close you can see the dots as a graininess.

I don't have any experience printing renders of any size, but I have printed photos anywhere from 4x6 inch (of course - who doesn't) up to 36 inches. The recommended PPI for "photo quality" is 300. For A3 this is roughly a 17 mega-pixel image, more than any camera I have. However, I've been experimenting with stitching multiple photos together to form very high-resolution panoramas. I have an image that is 150 mega-pixels - I haven't printed it yet.  I plan to print it at 6 feet by 2 feet, which is about 300 PPI. I plan to hang this in my upstairs hallway, where you will always be within a few feet when you look at it.

I like this megapixels chart - have a look.

http://www.design215.com/toolbox/megapixels.php

If you're not going to actually hold the paper, but rather hang it on a wall and view it from a distance, I think 150 to 200 PPI is acceptable for photos. I have a 6 megapixel photo in a 36 inch print that looks fine, because we don't stand 2 feet away from it.

However, if you want a render with incredible sharpness (usually not possible from a camera) then I'd stick with 300 PPI.

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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)