Why Mash Tun Sizing Matters
A mash tun is more than a bucket for grain and hot liquor. It is a heat vessel, a mixing chamber, and a filtering bed. The right size supports stable temperature, smoother stirring, and safer transfers. An undersized tun can overflow during dough in. An oversized tun can lose heat quickly when the grain bed is shallow. Good sizing starts with volume physics. Grain has mass and takes space. Water adds liquid volume. Dead space sits below drains. Headroom protects the brewer from splashing and foaming.
Planning Around Real Brewing Conditions
This calculator uses common brewing variables, but it also leaves room for process choices. A thick mash needs less strike water, yet it can be harder to stir. A thin mash improves mixing, but it demands more vessel capacity. Crushed malt usually displaces about 0.08 gallons per pound, or 0.67 liters per kilogram. Equipment design changes that number slightly. False bottoms, screens, and manifolds also change useful volume. Measuring your own tun once can improve every future batch.
Interpreting the Results
The recommended capacity is not just the liquid level. It includes grain displacement, dead space, and added headroom. The working mash volume shows the space occupied during conversion. Fill percentage compares that load with the vessel capacity you entered. A high fill value means careful stirring is needed. A low value may point to heat loss risk. Grain bed depth is useful when a diameter is provided. Very shallow beds can run fast, but they may filter poorly. Very deep beds can compact and slow runoff.
Better Brew Day Decisions
Use the result before buying equipment, scaling recipes, or changing mash thickness. Compare several grain bills. Save one result as a file for records. Export another for a brew log. Keep safety margins generous when brewing high gravity recipes. Extra headspace helps during stirring, recirculation, and temperature correction. The best tun is not always the largest one. It is the vessel that fits your recipe, method, and heat management plan. With clear volume estimates, the mash starts cleaner and ends with fewer surprises. Review the numbers again when malt crush, target gravity, or process temperature changes. Small checks prevent messy corrections.