Calculating dilution of gravity and drop in temp by adding water to chill my wort?

I'm interested to understand how to target a wort volume of a certain gravity so that when I use water of a certain temperature to chill my wort I will automatically reach the OG I target. So how water volumes dilute gravity and how cold water can lower my boiled wort. Anybody knows a software for that?

I don't think you are going to like how low your SG will go if you use enough cold water to get sufficient cooling. The equation for SG is:For temperature it is (approximately):
Brew on

You're missing a piece of information as well, IBUs. High gravity boils have a lower hop utilization, so you're getting less IBu per oz of hops by doing a concentrated boil.

Moreover, when you top off like this you cut your IBU by the ratio of the diluted volume to the original volume. Post boil 3G at 80 IBU, diluted with 2G of water, gives you 48 IBU.

Lastly, you're going to have an upper limit on your ibu of about 60 due to the fact that it's difficult to get 80-100 IBU in reality without doing hop shots or adding hop extract.

beersmith....

This may not be good advice, but what I do is start with my target volume and keep topping off along the way. That way I know that my volume is going to be constant throughout the process and your preboil gravity should the same as postboil. If my preboil gravity is off, I could top off a little more or less.