Calculate FLA From LRA

You can guess, but you cannot calculate.

Assuming you don't have a motor nameplate that gives you this information properly, and you have somehow measured the LRA (scary thought), you can reasonably guess that the FLA is 1/6th the LRA. But if you need to determine this for the purpose of selecting motor thermal overload protection, this is unacceptable. You need the real data.

Out of curiosity, how do you have the LRA but not the FLA?

If, by chance, this is a large chiller or refrigeration compressor, it's very common that those motors do NOT provide FLA data on the nameplate. It used to be allowed as "proprietary information" which forced you to get service from the chiller mfr. only. Now what they must do is provide something useful, so they use the term "MOP" on the nameplate with no explanation. That stands for Maximum Overcurrent Protection, meaning the OL device selection current. That's what you would use. Unfortunately that only started taking place a few years ago, there are many many chiller and compressor units out there with nothing useful on the nameplates. For those, your only choice is to call the mfr.