However, if you still want to calculate a federal prison sentence then there is no concrete method or formula but it depends on a number of factors which we can explain in the hope that it will deter you from committing a heinous act or maybe even considering lying to get a lighter sentence. One of which has to do with the degree of the crime.
There are various degrees of crime. The lower they are, the lighter the sentence and the higher they are the more severe the sentence. Lower degree crimes can result in anywhere between a month to a few years in prison. However, it depends on the judge and the jury as well as your lawyer. The case and facts themselves can be manipulated but in the end its those on the other side of the bench that decide your fate.
Your mental state at the time of the crime also plays a role. If you were not in control of yourself due to intoxicants or something along those lines then chances are that you will get a lighter sentence. Having said that, getting drunk and committing a murder or robbery does not guarantee anything, as the investigation will bring up a number of evidence that can be used against you. In any case, one can expect to be in jail for a number of years in any case.
Another factor to consider is your lawyer as well as the judge. The better the lawyer, the better your chance of maybe getting a lighter sentence. The same goes for the judge, he is there to simply execute the law but present a solid case and maybe you can get a lighter sentence.