system
A chat on subreddit /r/wallstreetbets
human
It's usually 85% of the value of the front month at-the-money straddle, but that site does some more complicated maths to get a 7 day implied move 
  
 e.g. add the price of the front month ATM call and the price of the front month ATM put, then multiply by .85 and divide by the actual SP if you want the percent 
  
 NFLX ATM call: 16.20   
 NFLX ATM put: 16.28   
 ATM straddle: 32.48   
 implied move: 27.61 (9.6%)

gpt
Thanks chief ..