There are several threads: https://community.airtable.com/search?q=word%20count
Look at the reply by Gareth (above) for a solution.
@Kaiti_Hill Looks like the quotes in the version above got mangled somehow. Some are straight, others are curled. Try copying this, which is the fixed version that I tested successfully:
LEN(Name)-LEN(SUBSTITUTE(Name," ","")) + 1