Looking for the correct standard size and dimensions. The Festival de Cannes websites says this:
Electronic, 300 dpi, 13 x 18 cm
Printed, Din A1, 59 x 84 cm
Is that the baseline standard? Roughly a 4 x 6 inch ratio? Neither size is coming up as a standard in the photo editing software I'm using.
Depends on its use. Remember, this same key art will be on the cover of your DVD, displayed full-size at theaters, and featured in your "look book" iPad sales presentation.
UK Quad Posters are 30x40 INCHES. US are different. I suspect European ones to be different sizing too. I think it's entirely dependent on the use, country, kind of promotion, etc. There isn't a one-size fits all.