I am wondering how to calculate check raise amounts in multiway pots.
For example, if everyone has 10k in chips and I want to check raise into a 4-way flop when the pot is 1.2k, how do I figure out my raise based on my opponent's bet and number of callers and the pot size?

Typically my c/r = (3 + # of callers) x Bet Size.

So if I check, the next guy bets 300 and there are 2 callers and I want to c/r I would raise to 1,500.

I sometimes lower it to (2.5 + # of callers) x Bet Size if I have under 30 BB's.

The pot size comes into play only if the original bet was extremely small compared to the pot. For me a typical bet is between 40% and 50% of the pot. If a guy bet 25% pot (blocker bet) I might c/r bigger than otherwise.

I'm more worried about effective stack sizes really. So if my c/r would commit >30% of my stack, I would typically shove unless there were some extraordinary circumstance (like I knew I would never be bluff re-raised or I knew that I would often be bluff re-raised.)