About this tool
The Mash Strike Water Calculator is a free, in-browser all-grain homebrewing tool that tells you how hot your strike (mash-in) water must be, and how much of it to use, to land your mash at the target rest temperature. Because the cool, room-temperature grain absorbs heat the instant it hits the water, the strike water always has to be several degrees hotter than the rest you want. Enter your grain weight, water-to-grain ratio, grain (room) temperature, and target mash temperature, and it returns the strike temperature and volume. Everything runs locally in your browser.
The strike temperature uses the standard infusion equation Tw = (0.2 / R) × (T_target − T_grain) + T_target, where R is the water-to-grain ratio in quarts per pound and 0.2 is the specific-heat ratio of grain to water. The strike volume is simply R × grain weight, reported in quarts, gallons, and liters. In metric mode the same physics applies with R in liters per kilogram and the constant 0.41 (that is 0.2 × 2.0864) so temperatures come out in °C. If you also enter a current mash temperature below the target, the tool sizes a boiling-water infusion for a step mash: V_add = (T_target − T_current) × (0.2 × grain + water already in mash) / (T_boil − T_target).
As a worked example, 10 lb of grain at 70 °F mashed at 1.5 qt/lb to hit 152 °F needs strike water at about 163 °F and 15 quarts (3.75 gal). Real systems lose a little heat to the tun and air, so if your mash lands a degree or two low, preheat the mash tun with hot water first or nudge the strike temperature up by 2–3 °F on your next brew to dial it in.