Short answer: efficiency is one division done three ways. Brewhouse efficiency = collected points ÷ potential points; conversion efficiency = how much starch became sugar; and lauter efficiency = collected ÷ converted. Because brewhouse = conversion × lauter, splitting them in Excel tells you whether a low OG is a mash problem or a sparge problem — instead of leaving you to guess.
This is the deep dive on use cases 2 and 3 from the 20 brewing calculations in Excel pillar: not just measuring efficiency, but decomposing it to find the leak. It’s the hands-on companion to brewhouse yield-loss analytics and ties straight into mash efficiency and extract yield.
Step 1 — potential and collected points
Maximum extract is the grain bill’s potential: each malt’s weight times its points-per-pound-per-gallon. Collected extract is what you actually got, from measured OG and volume:
potential =SUMPRODUCT(weights,PPGs) (10 lb pale × 37 = 370)
collected =(OG-1)*1000*gallons (50 × 5.5 = 275)
brewhouse_eff =collected/potential (275 / 370 = 74%)
That 74% is the headline — but it doesn’t say where the missing 26% went.
Step 2 — split conversion from lauter
Conversion efficiency is how completely the mash turned starch to sugar (a fine-crush, well-rested, correct-pH mash hits ~95%). Lauter efficiency is how much of that sugar you rinsed out. They chain:
after_conversion =potential*conv_eff (370 × 0.95 = 351.5)
lauter_eff =collected/after_conversion (275 / 351.5 = 78%)
So our 74% brewhouse efficiency is 95% conversion × 78% lauter. The waterfall makes the two losses visible side by side.
Step 3 — reconcile and diagnose
Add a “predicted OG” cell from your expected brewhouse efficiency and compare to actual:
predicted_OG =1+(potential*expected_eff)/(gallons*1000)
When actual falls short, the split tells you where to look. Low conversion (the mash made less sugar than it should) points at crush coarseness, mash pH, rest temperature or time. Low lauter (you made the sugar but didn’t collect it) points at sparge technique, grain absorption, or kettle/tun dead space — the same losses you sized in the mash water calculator. One sheet, and a missed OG becomes a named cause.
Where the decomposition gets fuzzy
Two honest caveats. First, conversion efficiency is hard to measure directly without a fine-grind lab test or a first-wort gravity reading, so most brewers assume ~95% and attribute the rest to lauter; if your real conversion is poor, the sheet will wrongly blame the sparge. A first-runnings gravity reading is the cheap fix — it splits the two for real. Second, PPG values are nominal — maltsters publish potential under lab conditions, and your actual extract depends on the specific lot, so treat the efficiency number as consistent-relative-to-itself rather than a universal grade. Track it across brews and the trend is what catches a drifting mill or a tired mash tun.
The bottom line
Efficiency is one division, but doing it three ways — brewhouse, conversion, lauter — turns “my OG was low again” into “my lauter efficiency dropped, check the crush gap.” Reconcile predicted against actual every brew, and the sheet stops being a scorecard and starts being a diagnosis.
Frequently asked questions
How do I calculate brewhouse efficiency in Excel? Brewhouse efficiency = collected gravity points ÷ maximum possible points. In Excel: =((OG-1)1000gallons)/SUMPRODUCT(weights,PPGs). For 5.5 gallons at OG 1.050 against 370 potential points that is (50×5.5)/370 ≈ 74%.
What is the difference between conversion and lauter efficiency? Conversion efficiency is how much of the grain’s starch the mash turned to sugar (typically ~95%). Lauter efficiency is how much of that sugar you actually rinsed into the kettle. Brewhouse efficiency is the two multiplied together, so a low number tells you which stage to fix.
Why did my original gravity come in low? Split the miss: if conversion efficiency is low, suspect crush, mash pH, or rest time; if lauter efficiency is low, suspect sparging, grain absorption, or dead space. Reconciling predicted against actual points in a sheet points you at the right cause instead of guessing.
Part of the Brewing Science & AI track.