OG in a carboy

Hi all, well today should be interesting. Not having room set up for a full ag set yet, I decided to get some practice in with the mini mashes until I do. Now with pure extracts I've been pretty much presuming the OG is somewhere within the anticipated since switching to a carboy for pirmary. With the mash of course that's not so presumable though, so I just wanted to check real quick to see if there is a given formula for measuring the gravity in the kettle and then topping in the carboy?

Off hand, I'd guess a ratio figgure would work say something like [email protected] + [email protected] = [email protected] but then again there's been stranger math used in brewing before.

That's right. When you're diluting, boiling, etc. It's easy to use 'gravity points'. Just take the number after the decimal point in your gravity and multiply it by the gallons. In your case 3*100=300 grav. points. To get your final gravity, take your gravity points and divide by the finished volume 300/5=60.

Works the same way for estimating OG from pre-boil volume. If you collect 8 gallons of wort at 1.040, you have 8*40=320 gravity points in your kettle. The OG of your batch will be 320 divided by whatever your post boil volume is. If you boil down to 6 gallons, your OG is 320/6=53, or 1.053.

Thanks much, shall put it in the calculations book

On a somewhat related note, know any good techniques for marking a carboy? So far I've been using masking tape but was hoping for a marker/pen of some sort, and thus far haven't found anything that wants to stay when washing.