💧 Sparge & Total Water Calculator

Enter your grain weight, mash ratio, and target pre-boil volume to calculate how much mash water and sparge water you need.

Grain Weight (lbs)

Mash Ratio (qt/lb)

Target Pre-Boil Volume (gal)

Grain Absorption Rate (gal/lb)

Splitting the water between mash and sparge

Mash water comes from your ratio, total water from the pre-boil target plus what the grain keeps, and the sparge is whatever is left over:

mash water gal  = (mash ratio qt/lb × grain lb) / 4
total water gal = pre-boil gal + (grain lb × absorption gal/lb)
sparge gal      = total - mash

Ten pounds of grain at 1.25 qt/lb is 12.5 quarts, or 3.13 gallons of mash water. The grain will hold 10 × 0.125 = 1.25 gallons, so a 6.5 gallon pre-boil target needs 7.75 gallons in total and 4.63 of those go on as sparge.

Setting the four inputs

Mash ratio takes 0.5 to 3 qt/lb. Most infusion mashes sit at 1.25-1.5; thinner mashes convert faster, thicker ones hold temperature better.
Absorption defaults to 0.125 gal/lb (half a quart per pound). A fine crush and a long drain gets closer to 0.10; a squeezed BIAB bag lower still.
Pre-boil volume is the figure in the kettle before you light it, so it must already allow for evaporation, kettle deadspace and trub. Boiling off a gallon an hour, 6.5 gallons pre-boil lands near 5 in the fermenter.

Grain	Mash water	Sparge	Total
8 lb	2.50 gal	5.00 gal	7.50 gal
12 lb	3.75 gal	4.25 gal	8.00 gal
20 lb	6.25 gal	2.75 gal	9.00 gal

A big grain bill at a thin ratio can need more mash water than the whole recipe uses. The page refuses that rather than showing a negative sparge: lower the ratio, or raise the pre-boil target.

Frequently asked questions

How much sparge water do I need for 10 lb of grain?

4.63 gallons, mashing at 1.25 qt/lb for a 6.5 gallon pre-boil. Heat it to about 170 °F and add it slowly once the mash has drained.

How much water does grain absorb?

Roughly 0.125 gallons a pound, which is why 10 lb costs you 1.25 gallons that never reaches the kettle. Report a squeezed bag as 0.10 and a well-drained cooler mash tun as 0.13.

What if I brew in a bag with no sparge?

Set the mash ratio high enough that mash water equals total water — for 10 lb into 7.75 gallons that is 3.1 qt/lb, just past the field's limit, so use 3 and top up the kettle with the small remainder.