>>3315804Determine viewing distance to know roughly how many ppi you need then divide the image's resolution by required dpi.
Example:
People won't get closer than 1m from the image so 180ppi are enough and you have a 6000*4000 image that does not require any croping:
6000/180 = 33.33'' (84.66cm)
4000/180 = 22.22'' (56.44cm)
Even at 300ppi you would get a 20''*13.33'' (50.8cm*33.86).
An A4 print at 300ppi only requires a 3,507*2,481 image.
