I ride a gravel bike but it's pretty much just a road bike now since the "gravel" here is beyond my abilities.

Anyway, I have a 46/36 in the front and an 11-40 in the back. I decided to get a compact crank (50/34), but realized I probably need a longer chain now since I'm adding 4 teeth.

Is there a rule of thumb that I can use to determine how many links I need to add? When I setup the 11-40, I used the whole length of KMC chain I bought. Of course, now I'm worried that the chain is too long since I lost 2 teeth on the smaller ring.