Mash Tun Calibration

Measure how much heat your mash tun absorbs with one test pour, then calculate the strike water temperature for that tun without preheating it.

Pour a measured volume of hot water into the empty tun at room temperature, close it and read the settled temperature: the drop shows how much heat the tun absorbs. A tun that cools 8 L of 80 °C water to 76 °C equals about 0.56 kg of water, so a 66 °C mash needs strike water about 2 °C hotter.

Reviewed by Diego Santiago, Professional Brewer

MetricUSImperial (UK)

1. Measure your mash tun

Hot water poured in (L)

About as much water as a typical mash

Hot water temperature (°C)

Measured just before you pour it in

Tun temperature before (°C)

Room temperature, with the tun empty

Settled temperature (°C)

After 5 to 10 minutes with the lid closed

Tun water equivalent0.563kg of water

2. Strike water for this tun

Grain (kg)

Total weight of the grain bill

Water-to-grain ratio (L/kg)

Usually 2.5 to 4 L/kg

Target mash temperature (°C)

Mash rest temperature

Strike water, tun at room temperature74.2°CStrike water, preheated tun72.2°C

Results are estimates provided "as is," for informational and planning purposes only, without warranties of any kind. Check them before you rely on them: you are responsible for decisions about your beer and equipment, including pressure and carbonation levels, the pressure ratings of your kegs and fittings, and any alcohol content you declare. Use of this calculator is subject to our Terms and Conditions.

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How the tun is calibrated

When hot water is poured into a tun at room temperature, the heat the water loses is the heat the tun gains. Expressing the tun as an equivalent weight of water:

M_t = \frac{W\,(T_h - T_e)}{T_e - T_0}

where $M_t$ is the tun’s water equivalent, $W$ the weight of the hot water (its volume × 0.985 kg/L), $T_h$ its temperature, $T_0$ the tun’s starting temperature and $T_e$ the settled temperature.

The strike water then has to heat the tun as well as the grain. Adding the tun to John Palmer’s strike water equation:

T_w = \frac{0.4 + M_t / G}{R}\,(T_2 - T_1) + T_2

where $G$ is the weight of grain, $R$ the water-to-grain ratio by weight, $T_1$ the grain and tun temperature and $T_2$ the target mash temperature. With a preheated tun, $M_t$ is 0 and the equation is Palmer’s.

For example, 8 L of water at 80 °C poured into a tun at 20 °C that settles at 76 °C gives a water equivalent of about 0.56 kg. For 4.5 kg of grain at 3 L/kg and a 66 °C rest, the strike water for that tun at room temperature is about 74.2 °C, against 72.2 °C for a preheated tun.

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Sources

John J. Palmer. How to Brew, Brewers Publications, 2006. Strike water equation, with grain at 40% of the heat capacity of water and hot water at 0.985 kg/L (chapter 16, Infusion Calculations, updated 2025), which this calculator extends with the tun's water equivalent; 3rd edition, online version with the author's updates.

Frequently asked questions

Why calibrate a mash tun?

A cold tun absorbs heat from the strike water, so the mash comes out cooler than planned. Measuring the tun once tells you how much heat it takes, and the strike water temperature can then account for it every brew day.

How do I take the measurement?

Leave the empty tun at room temperature and note that temperature. Heat a measured volume of water, about as much as a typical mash, note its temperature and pour it in. Close the lid, wait 5 to 10 minutes, stir and note the settled temperature. Enter the four values.

What is a water equivalent?

The weight of water that would absorb the same heat as your tun. A water equivalent of 0.5 kg means the tun takes as much heat as half a liter of extra water at the same temperature.

Should I still preheat my tun?

Preheating gives the most consistent results, and with a preheated tun you can use the plain strike water temperature. Calibration is for brewers who mash into a tun at room temperature.

Why does my result change between measurements?

Heat also escapes through the lid and walls while the water settles, and that loss is counted as part of the tun. Use the same volume and waiting time each time, and average two or three measurements.