BIAB Calculator (Brew In A Bag Water)
Full-volume Brew In A Bag water: total strike water, mash volume for kettle fit, strike temperature and pre-boil volume - no sparge.
Strike water = total water because BIAB has no sparge. Check the mash volume against your kettle capacity (leave a few litres of headroom). Strike temperature is a starting point - preheat the kettle and stir well, then adjust to hit your mash target.
How it works
Full-volume BIAB uses one lot of water for the whole brew, so we add up everything that leaves the kettle - your target batch, evaporation during the boil, water the grain soaks up, and any trub/dead loss - to get the single strike volume. Mash volume adds the space the grain itself occupies so you can confirm the mash fits. The strike temperature uses the same heat-balance as the strike water calculator, at the water-to-grain ratio your full volume implies.
total (strike) water = batch + boil-off + grain absorption + losses
mash volume = strike water + grain × 0.67 L/kg (displacement)
pre-boil = batch + losses + boil-off
strike °C = mash°C + (0.40 / ratio) × (mash°C − grain°C)
Efficiency and evaporation vary between systems, and squeezing changes grain absorption, so treat these as close estimates and fine-tune to your own kit.
Sources: full-volume BIAB method per Brewer's Friend and Priceless Brewing's BIAB calculator; strike-temperature heat balance per John Palmer, How to Brew.
Frequently asked questions
- What makes BIAB water different from a normal calculation?
- Brew In A Bag is full-volume, no-sparge: you put all your water in the kettle at once and mash the grain in a bag. So your strike water equals your total water - there is no separate sparge. The tool adds up batch size, boil-off, grain absorption and any losses to give that single all-in number.
- Should I squeeze the bag?
- Squeezing recovers wort the grain would otherwise hold, so it lowers your effective grain absorption (this tool defaults to about 0.8 L/kg for a squeeze, versus ~0.96 for a lautered mash). Squeezing raises efficiency and there is no downside for tannins at mash temperatures - lower the absorption figure if you squeeze hard.
- Will my mash fit the kettle?
- The mash volume figure is your strike water plus the space the grain itself takes up (grain displaces roughly 0.67 L per kg). Compare it to your kettle capacity, leaving a few litres of headroom for a boil, to check the full-volume mash fits before you start.