Immigration and customs

You will go through immigration in Frankfurt. How much time to allow between connections? I will leave that answer to others who have transited through Frankfurt. We recently went through immigration in Munich with a 40 minute connection to Copenhagen and made it easily. Yes, that was close but I got a really good deal on the airfare and there were more flights after that that we could have been placed on. Plus I planned our trip to arrive a day earlier in case we missed our Munich to Copenhagen connection. If your reservation is booked on one ticket, the airline is required to get you to your destination. All that being said, I would build in more time for the connection (at least 2 to 3 hours) to be safe.

Yes, you will go through immigration, customs is a non-issue time wise, basically a passport check, maybe a question or two and on your way. Not sure how Frankfurt is set up, but typically you will want to look for the passage or hall with a sign indicating connecting flights, rather than following the majority of people headed for immigration and the exit. That way you stay airside and likely will not have to go through Security. Some airports everybody goes through immigration first then splits into connecting and exit/baggage claim; other airports split before immigration.

It sounds like you do not yet have tickets, if you have a choice, two hours is plenty, an hour probably would work OK, as the previous poster mentioned, if there are frequent flights, you can afford to be optimistic and pick a shorter transfer, you will get to Munich regardless.

When we have passed through Frankfort it has taken less than half hour... Just follow the signs to "Connecting Flights" and once through Passport control follow the signs...

The airlines that book you through know how much time it should take.

Don't go out the obvious door past Passport Control in your sleepy haze like I once did and found myself outside and needing to go back through Security....

Immigration (passport checks) will take place at Frankfurt. If this is one ticket, you would not have been sold the ticket if it wasn't enough time.

Customs is the check on your goods, it can only happen after you get your bags back. "Our bags will be checked through to Munich." - so customs will be at Munich. It is a random stop only, takes zero time.

Official transferring info of FRA.

Time shall depend on airline of transatlantc flight which we do not know.

"Don't go out the obvious door past Passport Control in your sleepy haze like I once did and found myself outside and needing to go back through Security...."

You too? In my sleepy haze, I took the long escalator down to baggage claim instead of the shorter one to the domestic terminal area. So, I had to go back through security (normally not needed at this airport for this kind of transfer). I still made my next flight without difficulty.

To the OP: I don't know the minimum "legal" connection time in Frankfurt for this kind of flight. But, as long as you've booked that much time or more, and are all on one ticket, don't worry. If you miss the connection, you will be put on the next available flight. From Frankfurt to Munich there are multiple frequent flights every day, so you will definitely get to Munich that day.

What airline(s) are you using? If your bags will be checked through to Munich, my guess is you are flying Lufthansa or a Star Alliance airline. With luck your flight might arrive at Concourse Z and depart from Concourse A. A and Z are in the same building, on separate floors. If you arrive at Z, you'll go through passport on you way down to A without going out of security. When we arrived at Concourse Z on a flight from the US (not transferring) five years ago, we had go pass through passport control to Concourse A before we could exit security and the building from Concourse A.

But check on the arrival concourses using the Frankfurt airport website.