There are at least 73 different types of synesthesia:
Data is based upon files on 1143 individual synesthetes.  The numbers given are the percentage of synesthetes who have the given specific type, not the percentage of the general public.  About 3.7% of the general public has some form of synesthesia. Thus, for example, the ratio of people with 'graphemes to vision' synesthesia to the general population is about 1 out of every 44 people; or, there are currently about 162 million people in the world with 'graphemes to vision' (e.g., "colored letters and numbers") synesthesia.
Last updated: 15.April.2016
***** = insufficient data
Demographic aspects of synesthesia
***** indicates "insufficient data" 
Seventy-three types of synesthesia. The left hand column is inducers; the top row is concurrents. White indicates the type has been documented; red indicates no case of this type has yet been recorded; black signifies that this would not be a type of synesthesia.