Grain Shrinkage Calculator

Grain absorbs water during the mash and holds onto it in the spent grain bed, so that water doesn't make it into your kettle. A typical absorption rate is about 0.5 quarts (0.125 gallons) per pound of grain, though it varies by crush and mash thickness — most brewers land between 0.4 and 0.7 qt/lb.

Your pre-boil volume needs to account for how much water boils off during the boil, plus any loss to trub (hop and protein sediment) and your chiller/hose dead space, so that after boiling and cooling you actually end up with your target batch size.

About 1-1.5 gallons per hour for a typical homebrew kettle and burner setup, though it depends heavily on your kettle diameter, boil vigor, and altitude. Measure your own system's rate for the most accurate results over time.

Yes, if you have it — every system absorbs water slightly differently based on grain crush, mash tun design, and lautering method. Track your actual strike/sparge volumes vs. what you collected over a few batches and use that rate here for better accuracy.

Strike water temperature = (0.2 ÷ mash thickness in qt/lb) × (target mash temp − grain temp) + target mash temp. Because water loses heat to the (usually cooler) grain when they mix, your strike water needs to be noticeably hotter than your target mash temperature — often by 10-15°F depending on your thickness and grain temperature.