I decided to reverse engineer the Quick Water Calculator just to find out how it worked out the values that always seemed to be different from those I plumbed into the Recipe Editor. I could never rationalise the Sparge Water requirements given my input values for Mash and Sparge values. So this is how I think it works but I'm willing to be proved wrong. This is what I discovered: As you may have already worked out the starting point is what you choose to set for the recipe TARGET and BATCH SIZE. The Estimated Boil Size is not so important at this point but will make a difference as we shall see later. The next important value that is to be considered is the Mash Thickness (as you would imagine) that, together with the Weight of the Fermentables, defines the amount of Strike Water required. There is some weird calculation in the background when the volume exceeds the Mash Tun limit (as set in the Profile) but I have yet to figure out what the formula is - it is NOT just Batch Size + Grain Absorbtion + MT Dead Space. There are six values set in your profile that are used in the calculations: A. Grain absorption losses B. Mash Lauter Tun dead space C. Boil off losses D. Kettle dead space E. Hops absobtion losses F. Misc. Losses Additional values used are: G. Batch Size H. Total Fermentable Weight (Grains Only - even if marked Late Addition) I. Starting Mash Thickness (in Mash Guidlines section) What is NOT used are the values you put in for Mash and Sparge entries in the Mash Guidelines. Some intermediate calculations are made using the values above. J. Strike Water = Fermentables x Starting Thickness (= H x I) K. First Runnings = Strike Water - (Grain Absorbtion + MT Dead Space) (= J - (A+B)) If we work with some real values it might be easier to understand. (I hope!) Assume: A. Grain absorption losses 3.5 B. Mash Lauter Tun dead space 1.3 C. Boil off losses 3.7 D. Kettle dead space 1.6 E. Hops absobtion losses 0.6 F. Misc. Losses 1 G. Batch Size = 20 lt H. Fermentables = 3.5 kg I. Thickness = 3 liters/kg J. Strike Water 10.5 K. First Runnings 5.7 For the Target set to KETTLE Amount in Kettle = Batch Size + Boil off Losses (= G + C) = 20 + 3.7 = 23.7 Sparge Water Volume = Amount in Kettle - First Runnings (= G + C - K) = 23.7 - 5.7 = 18 litres Total Water Required = Strike Water + Sparge Water = 10.5 + 18 = 28.5 litres For the Target set to FERMENTOR Amount in Kettle = Batch Size + All Kettle Losses (= G + C + D + E + F) = 20 + 3.7 + 1.6 + 0.6 + 1 = 26.9 Sparge Water Volume = Amount in Kettle - First Runnings (= G + C + D + E+ F - K) = 26.9 - 5.7 = 21.2 litres Total Water Required = Strike Water + Sparge Water = 10.5 + 21.2 = 31.7 litres Deselecting the Late Additions check box will increase the Boil Gravity and therefore increase the calculated IBU values it does not affect the Mash and Sparge calculations. After getting the results from the calculations you can then put the Boil Size and Mash and Sparge volumes into the recipe - it should all make sense now. Adjusting the Boil Size to the the calculated Amount in Kettle will modify the Boil Gravity and therefore modify the calculated IBU values. If you don't do this step the recipe will not show the correct IBU value. I hope this is of some help to those who, like me, wondered how the quick calculator worked and the values never look like what was expected.