See here: https://developers.themoviedb.org/3/configuration/get-api-configuration
These are official sizes. Some older ones may still work. But they can die at any time.

images  
base_url    "http://image.tmdb.org/t/p/"
secure_base_url "https://image.tmdb.org/t/p/"
backdrop_sizes  
0   "w300"
1   "w780"
2   "w1280"
3   "original"
logo_sizes  
0   "w45"
1   "w92"
2   "w154"
3   "w185"
4   "w300"
5   "w500"
6   "original"
poster_sizes    
0   "w92"
1   "w154"
2   "w185"
3   "w342"
4   "w500"
5   "w780"
6   "original"
profile_sizes   
0   "w45"
1   "w185"
2   "h632"
3   "original"
still_sizes 
0   "w92"
1   "w185"
2   "w300"
3   "original"

Thanks a bunch for your response!!