This calculator turns your hydrometer readings into a clear efficiency picture. Enter your grain bill and the gravities and volumes you measured, and it reports brewhouse efficiency plus the pre-boil and post-boil figures so you can see exactly where sugar is being lost.
How it works
Every malt has a maximum extract potential in PPG — gravity points per pound per gallon at 100 percent efficiency. The maximum points your grain bill could yield is:
max points = PPG × grain pounds
The points you actually collected are measured gravity times volume in gallons:
actual points = (measured gravity − 1) × 1000 × volume (gal)
Efficiency is simply the ratio:
efficiency = actual points / max points × 100%
Applying this at the pre-boil sample gives your effective mash-plus-lauter efficiency before evaporation. Applying it at the post-boil sample confirms the final yield into the fermenter. Because boiling only removes water, the two percentages should agree closely; a large gap signals a measurement error.
Worked example
A 5kg grain bill at 37 PPG could yield 37 × 11.02 = 408 maximum points (5kg is about 11.02 lb). If you collected 26L of pre-boil wort at 1.042:
actual points = 42 × (26 / 3.785) = 42 × 6.87 = 288.5 points efficiency = 288.5 / 408 = 70.7%
That is a healthy batch-sparge result. If the post-boil reading (say 20L at 1.055) gives the same ~71 percent, your measurements are consistent.
Tips and notes
- Always cool your sample to your hydrometer’s calibration temperature (usually 20°C / 68°F), or apply a temperature correction — warm wort reads low.
- Refractometers need a wort-correction factor (typically divide Brix by about 1.04) before fermentation; this tool expects specific-gravity input.
- If conversion is your bottleneck, the pre-boil efficiency will be low even with a generous sparge — fix the crush and mash first.
- Track this number across brews; a stable efficiency lets you scale recipes reliably with the grain bill optimizer.