I think judging your level base on your blitz is highly inaccurate. Especially if you are trying to compare your online blitz to your OTB regular. I'll give you an example.
There has been a lot of times where I have witnessed people play friendly blitz. On pretty much every level except maybe 2300+. You have people who will quite often show really poor judgement in blitz. Heck even losing to much lower competition because they are younger and faster. On the other hand, in the same tournament watching those people most of them performed much higher in the OTB regular play setting. Several of them played blitz so poorly that they lost to most of the people in the tournament and then go on to win clear first in their sections. As much as people believe it can translate it can't.
Now.. IN general if you "AVERAGE" a certain rating it's a good chance that you can go by the 50/100 rule. Or the 100/200 rule depending on which one you want to apply. What this means is, if you want to know what level you are you can apply one of those two rules and be relatively accurate across multiple pools. I would suggest that you apply the 100/200 rule to transfer between pools. The reason is: The 50/100 rule is usually used within a pool to determine if players are relatively equal. Whereas most of the time the 100/200 rule is used to determine equality between pools.
What is the rules I mention exactly you ask? Basically you take a rating. You ADD the rule up or down to it. So let's take my rapid rating and apply it to my
chess.com rapid. If I apply the 100/200 rule I am 2154 right now. So I should be 2254-1954
chess.com. If you look at my
chess.com rating right now:
www.chess.com/stats/live/rapid/encephaloceleYou can see that I am 2084. So I fall within the 100/200 rule.
My USCF has dropped unfortunately because I need to get my killer instinct back in OTB play. I have been failing both with my attention and my health to sit long. I am working on that. However.. I am at my general low right now. I hit 1895? Maybe 1897? Mostly because I resigned my last two games out of anger. However I am usually consistenly over 1950. And I have extremely recently like even as soon as right after the first pandemic lockdown lift around 2000-2010. And I have been as high as 2057. If you discount my failure related to trying to get back into OTB shape, my USCF also falls in the 100/200 range.
About my FIDE rating:
At the moment my FIDE does not, but I am fresh out of getting my first rating. I still need to get out of my provisional status. It's possible I could drop the FIDE rating lower and it would stay outside of the 100/200 range but I have a reason for that. In the US there is a lot of people who are under rated related to the lack of tournament play in the US. We have even seen recent hotshots in our area have massively under rated players. A few years ago a kid about 13-14 had a USCF rating of 2450 with a FIDE rating of about 1450. We laughed at it when we saw it, but he went on the place in the top 20 players in that tournament in the open. That is obviously the most extreme example, but this proves true a lot. The average FIDE class player will have a rating gap of about 300-400 points until they reach the level to enter open tournaments freely and they play often. I never trust FIDE ratings in the US under 2200.
Conclusion: If you have not noticed I left out an important point in all of this. That is that you can apply the 100/200 rule to ALL of the ratings. And it will be relatively accurate. Notice I said "relatively". And if you apply this rule to my USCF it negates my excuse sort of with the FIDE rating. ;-) If we apply the 100/200 rule to my USCF right now, my Lichess rapid rating is slightly too high, but my FIDE rating falls in line. I still can negate the "CURRENT" FIDE rating based on my provisional status, but if I am outside my provisional status I have to apply the rule regardless of where it is at that time. So look at the difference between my ratings. The ratings that fall outside of the 100/200 rule only fall out of that rule within the 50/100 rule. And this is consistent with all of my ratings currently. You can theoretically use this system to estimate ratings. And you can logically use a correction of about 50 points average. So if your rating here averages let's take yours 2100? If we assume we can apply this rule to your rapid we can say your rapid is about 1900-2300. Give or take 50 points. In general it should be somewhat accurate. Unless there is some other thing that hinders a particular rating. Like some people can play OTB but something about computers make them unable to perform online and vice versa.
Sorry for the book.