Strike Water & Mash Temperature Calculator

How this works

Mashing works by holding crushed grain at a target enzyme-active temperature for long enough to convert starch into fermentable and unfermentable sugar. The water you add to the grain (the "strike water") has to be hotter than your target mash temperature, because mixing it with room-temperature grain pulls the combined temperature down — how much hotter depends on how much grain you're heating relative to how much water is doing the heating.

This calculator uses the standard published strike-water formula from John Palmer's How to Brew, reproduced in essentially every homebrew mash calculator: StrikeTemp = (0.2 / R) x (targetMashTemp - grainTemp) + targetMashTemp, where R is your water:grain ratio expressed in quarts per pound. The constant 0.2 comes from the approximate specific heat of malted grain relative to water — grain absorbs roughly a fifth as much heat per degree as the same mass of water, which is why a thin mash (a high ratio, lots of water relative to grain) needs a much smaller temperature overshoot than a thick mash (a low ratio) to hit the same target.

The calculator runs the maths in the formula's native units (quarts per pound, Fahrenheit) internally, converting your metric inputs and outputs at the boundary — the published constant is the trustworthy part of this formula, so it's used exactly as published rather than re-derived in different units, which is where a conversion error could quietly creep in.

Ratio matters more than people expect

A thicker mash (lower L/kg or qt/lb ratio) requires a bigger strike-temperature overshoot to hit the same target mash temperature, because there's less water carrying the heat relative to the grain absorbing it. Typical ratios run 2.5-3.5 L/kg (roughly 1.2-1.7 qt/lb) — thinner mashes run cooler strike-water overshoots and lauter faster, but can also reduce enzyme concentration slightly; thicker mashes concentrate enzymes more but need hotter strike water and can be harder to stir evenly.

Reading the result

If your actual mash temperature consistently lands lower than this calculator's prediction, the most common causes are an under-insulated mash tun losing heat to a cold room or cold vessel walls, or grain that was colder than you estimated (grain stored in a cold garage or basement can be 15-20°F below "room temperature" without it being obvious by touch). Measure your grain temperature directly with a thermometer rather than assuming it, especially in winter.

A worked example

5 kg of grain at 20°C, targeting a 67°C mash at a 2.9 L/kg ratio, needs strike water heated to 73.8°C — a roughly 6.8°C overshoot above the target, which is a fairly typical figure at this ratio. Thin that same mash out to 3.5 L/kg and the required overshoot shrinks; thicken it to 2.2 L/kg and the required overshoot grows, for the identical grain weight and temperature gap.

Preheating your mash tun

A cold mash tun (especially an uninsulated cooler or an all-metal vessel that's been sitting at room temperature) absorbs some of your strike water's heat on contact, pulling the actual mash temperature below what this calculator predicts even with perfectly accurate inputs. Many brewers preheat their mash tun with a splash of near-boiling water, swirled and drained immediately before adding the real strike water, specifically to cancel this effect out — the calculator's own prediction assumes the vessel itself isn't absorbing a meaningful share of the heat. An insulated cooler-style mash tun needs this less than a bare metal vessel, since it loses far less heat to the surrounding room over the course of a typical mash rest.