Any BIAB dunk sparge calculator out there that people have proved?

May need to just study my brew house efficiency more after the next couple batches but it seems I must mash thick and sparge more since my volumes are too high even with a 90 min boil for pils base recipes.

Using a standard mash/ sparge calc from brew365 with an 18 lb grain bill sent me almost 4 gallons over desired preboil volume!

This certainly involves squeezing the bag after a long drain whereby the grain absorption must be significantly less than a standard lautering process.

Thanks all!

A lot of use calculators allow you to adjust parameters including absorption. Using your volumes from the last batch, you should be able to figure out your actual absorption and plug that value in the calculator.

I actually use the Brewzor calc on my Android and it is pretty much spot on every time. But you have to know your boil off rate and enter your pre-boil volume so that may not help you find the error. I am a little confused at how you could be 4 gal off... that's almost 50%. That said, I have never noticed a measurable difference in loss between doing biab (dunk and pour) vs my cooler tun.

4 gallons over? This is a huge disparity. Are you certain that you made no errors in how you entered your recipe? I have never used Brew365 but a fairly common absorption rate assumption is around 0.1 gal/lb. This is the general rule that I follow and I have never had any issues where absorption has not been fairly consistent with that assumption.

Looking back I don't know how I came up with 4.2 gallons. I really must have entered the data wrong on the brew365 app. Repunching the numbers it gives me 2.8 gallons sparge (which in hindsight wouldn't help me to dunk with that much of a grist). In anycase the gravity turned out spot on since I added dme to make up the volume error and did an 8 gallon batch instead. I must pay closer attention next time around.