Trying to sort out a water chemistry/calculator question

[hedo-rick]

I've always (with good good results) prepped 10 gallons of water for my 5.5-5.75 gallon batches and calculated the final mineral content based on my final fermenter volume...something like this
...7.59 (pre-boil) / 5.5 (fermenter) * 58 ppm CL (10 gallons treated water) = 80.04 ppm CL (finished beer)

I can't help but think I could simplify my process by plugging in my mash water volume, but subtracting my grain absorption and boil off volume from my total sparge water volume, then adding my mash salts giving me my final mineral content based on the fermenter volume...something like this for a beer I'm planing
Total Water: 8.8 gallons
Mash Water: 4.1 gallons
Sparge Water: 4.78 gallons - 1.29 gallons (grain absorption) - 1.84 gallons (boil off) = 1.65 gallons entered for sparge volume. Giving me a total of 5.75 gallons in the fermenter.

Am I completely off here? Am I going in the right direction? Am I missing something?

 

[Nosybear]

There's a calculator on this site for that.... I'd throw in a quart or so for "dead space" losses in the mash tun, spillage, samples and so forth but you're on the right track. If you rack to the fermentor rather than dumping everything in, you'll need to account for the wort left in the kettle. There's a small amount of wort lost to the hops - unless you're putting lots of hops in, likely too small to track. And yes, you're on the right track.