How many MegaPixels required to product an acceptable poster print?

[funlovephotography]

I'm coordinating a photographic display for a charity and working with a range of amateur to pro photogs. We need to print posters at 36"x48". What MP (or other guideline) do I need to give photographers for minimum gear requirements to print acceptably at this large size?

I'm not looking for DPI math, but a practical answer that account for viewing distance, etc.

Thanks.

 

Edited July 11, 2017 by funlovephotography

[Damien Symonds]

Six.

https://www.damiensymonds.net/2011/02/printing-big.html

https://www.damiensymonds.net/art_enlarge.html

https://www.damiensymonds.net/2014/03/how-aggressively-can-i-crop.html

https://www.damiensymonds.net/2015/10/noise-reduction-and-sharpening-leap-of.html