Newbie All Grain Question

I did my second all grain batch the other day. The NB Wee Heavy.
It was running late at night by the end of the brew day and I forgot to measure my gravity before I pitched my yeast and headed to bed.
I did however take a reading with cooled wort while I was doing my boil.
The pre-boil wort SG measured 1.074 with a recipe expected 1.083 SG.

Is there a way to estimate what the post boil SG would have been?

I started with 6.2 gallons when I began my boil and I boiled down to 5.4 gallons.

FWIW, the batch is gurgling away during fermentation. Pretty intense.....

PbG * PbV / V

Should get you the post boil gravity. V is post boil volume, PbG is preboil gravity, PbV is preboil Volume.

Umm, I don't think that works.
I get 1.2331 for a SG
1.074 *(6.2/5.4) = 1.2331
If that was the case, I would be high on life and beer
Any other ideas, or just don't forget next time.....

Take the 1 off, and just use the decimal portion. "070" would be 1.070, etc.

1.085 at 5.4 gallons post boil

This is able to be calculated bc the total gravity of your wort stays constant through the boil. Therefore, V1*gravity1=V2*gravity2.

In your case, V1 is 6.2 gallons, gravity1 is 74 (use the numbers after 1.--- in your read specific gravity) and V2 is 5.4. Solve for gravity2 = 85. Therefore your OG post boil is 1.085

Thanks for the help!