Mash Size

BrewCo Brew Tools

Use this free mash size calculator to check your mash tun is big enough before brew day — working out the total volume of water and grain combined.

How to use it

  1. Weigh your total grain bill.
  2. Decide your mash thickness — typically 2.5–3.5 L per kg of grain.
  3. Read off the total mash volume, and check it against your tun's capacity.
Typical range: 2.5–3.5 L/kg. Grain itself takes up roughly 0.67L per kg of space.
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Why does mash tun size matter?

If your grain and water combined don't fit your tun with enough headspace for stirring, you'll struggle to mash properly — and risk boiling over or spilling. Checking this before brew day, especially for bigger or higher-gravity batches, saves a stressful surprise partway through your mash.

More free home brew calculators

Browse our range of mash tuns and all-grain brewing gear at BrewCo UK, Sowerby Bridge.

How to check your mash tun is big enough

What it does: this calculator works out the total volume your mash will take up, water plus grain, so you can check it fits in your mash tun before brew day.

How to use it: enter the total weight of your grain bill and your mash thickness in litres per kilo. Most brewers use 2.5–3.5 L/kg. Compare the answer with your tun's working capacity.

The formula in plain words: the water volume is grain weight multiplied by mash thickness. The grain itself takes up about 0.67 litres of space for every kilo. Add the two together for the total mash volume.

Worked example: 5 kg of grain at 3 L/kg needs 15 litres of water. The grain adds about 3.35 litres, so the mash takes up about 18.4 litres. Leave a little room for stirring, so a tun with at least 20–22 litres of usable space is sensible.

Next, find the right water temperature with the strike temperature calculator.

Frequently Asked Questions
What mash thickness should I use?
Around 2.5–3 L/kg is a good starting point for most beers. A thinner mash is fine in all-in-one systems, which often run nearer 3.5–4 L/kg.
Why does grain take up less space than its weight in water?
Water fills the gaps between the grains, so a kilo of crushed malt adds only about two-thirds of a litre to the total volume once it is mashed in.
What if my mash is too big for my tun?
Use a thicker mash and sparge with more water, brew a smaller batch, or brew a lower-gravity beer that needs less grain.