CanadaTier 2
Boil-off calculator
Pre-boil volume and gravity in. Post-boil volume and concentrated gravity out.
Free·No sign-up·Last checked 2026-08-27
Formula
Post-boil volume = pre-boil volume − (evaporation rate × boil hours)
Post-boil gravity points = pre-boil gravity points × pre-boil volume ÷ post-boil volume
Worked example. 23 L at 1.038 boiled 60 min at 3.8 L/hr → 19.2 L post-boil at 1.046.
Questions
Boiling removes water as steam but not the dissolved sugar, so the same total gravity points end up concentrated into a smaller volume — that's why post-boil OG reads higher than pre-boil gravity.
Measure your kettle volume before and after a timed boil on your own setup. It depends on kettle diameter, boil vigor, altitude and lid use, so a measured rate is far more accurate than any default.