Boiloff Calculator
Calculate your boiloff rate by entering your pre-boil and post-boil volumes. Helps you calibrate your system for consistent batch sizes.
Measure boiloff so your batch volume lands on target
Use the boiloff calculator to estimate how much wort your kettle loses during the boil, after accounting for boil time and wort shrinkage.
Example boiloff check
If you start with 6 gallons before the boil and finish with 5 gallons after a 60 minute boil, enter both volumes and the boil time to estimate your system's hourly boiloff rate.
- Measure pre-boil volume before the wort reaches a rolling boil.
- Measure post-boil volume after flameout, using the same volume markings if possible.
- Use the calculated boiloff rate in future recipe and sparge-water planning.
Watch for: Boiloff changes with kettle shape, burner power, weather, and boil intensity, so recheck it when your setup changes.
Frequently asked questions
Why measure boiloff?
Boiloff affects pre-boil volume, final batch size, gravity concentration, and how much wort reaches the fermenter.
Should I measure hot or cooled wort?
Use consistent measurements. The calculator includes wort shrinkage, so record volumes carefully and account for cooling when needed.
Is boiloff always the same?
No. It varies with boil vigor, kettle diameter, lid use, humidity, and burner output.
Where should I use this result?
Use it in recipe planning and the sparge water calculator so your water volumes match your real brewing system.
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