How is sparge water volume calculated?

First the mash water is the grain weight times the mash ratio. From that, the calculator subtracts grain absorption and mash tun dead space to find the wort collected from the mash. The sparge water is whatever is still needed to reach your target pre-boil volume.

How much water does grain absorb?

Crushed malt absorbs roughly 1.04 litres per kilogram, or about 0.125 gallons per pound. This water stays trapped in the grain bed and never reaches the boil kettle, so it must be accounted for separately from the wort you collect.

What is mash tun dead space?

Dead space is the volume of wort that sits below your false bottom or pickup tube and cannot be drained. It is a fixed loss for your equipment, typically a few tenths of a litre to a litre, and is added to the absorption when working out how much you actually collect.

What if the calculator says no sparge is needed?

If your mash water alone already exceeds the pre-boil target after absorption and dead space, the sparge volume is negative. That means you are effectively doing a no-sparge or full-volume mash. Use a thinner mash or simply mash with your full water charge and skip the sparge.

Does this work for batch sparging and fly sparging?

Yes. The total sparge volume is the same for both methods. For batch sparging you split that total into one or two roughly equal additions, while for fly sparging you run it in slowly to match the wort flowing out. The number this tool gives is the combined sparge water either way.

Sparge Water Volume Calculator

The Sparge Water Volume Calculator works out exactly how much sparge water you need to rinse your grain bed and reach your target pre-boil volume. It accounts for grain absorption and mash tun dead space, the two losses that catch out most new all-grain brewers, so you collect the right amount of wort every time.

How it works

On brew day, water splits into several streams. The mash water (also called strike water) goes in first to convert the starches. Some of that water is absorbed by the grain and never comes back, and a little is trapped below the false bottom as dead space. The rest drains out as wort. Whatever volume is still missing from your pre-boil target is made up with sparge water:

Mash water    = grain weight * mash ratio
Wort from mash = mash water - (grain * absorption) - dead space
Sparge water   = pre-boil target - wort from mash

Grain absorption is about 1.04 litres per kilogram (0.125 gallons per pound), and dead space depends on your mash tun. The calculator shows each step so you can see where every litre goes.

Worked example

A 5 kg grain bill mashed at 3 L/kg, with 1.04 L/kg absorption, 0.5 L dead space, targeting 28 L pre-boil:

Mash water = 5 * 3 = 15 L
Grain absorption = 5 * 1.04 = 5.2 L
Wort from mash = 15 - 5.2 - 0.5 = 9.3 L
Sparge water = 28 - 9.3 = 18.7 L

So you would heat 15 L of strike water and 18.7 L of sparge water, for 33.7 L total on the day.

Tips and notes

If the result comes back negative, your mash water alone already exceeds the pre-boil target, which means you are doing a no-sparge or full-volume mash, so simply skip the sparge. For batch sparging, split the sparge total into one or two roughly equal pours and stir well before draining each. For fly sparging, run the sparge water in slowly so the level stays a centimetre or so above the grain bed while wort drains out at a matching rate. Recalculate whenever you change grain bill size or mash thickness, since both shift the balance between mash and sparge water.