Brewhouse Efficiency: How to Calculate It

You’ve finished your brew day, checked the original gravity, and realized your numbers don’t match the recipe. Maybe you expected 1.052 but measured 1.046. Or perhaps your gravity looks good, but you collected less wort than planned. What happened?

Before changing your grain bill, look at brewhouse efficiency. It tells you how much of the grain’s potential extract actually made it into your fermenter. Understanding it helps you predict original gravity, plan ingredient quantities, and repeat your best batches.

The goal is not to chase the highest possible percentage. The goal is to know what your own system can reliably deliver.

What Is Brewhouse Efficiency?

Every malt contributes a potential amount of soluble extract. During mashing, enzymes convert starch into sugars; during lautering, the brewer separates sweet wort from the grain. Additional wort may be lost to the kettle, trub, hops, piping, and transfers.

Brewhouse efficiency compares the extract collected in the fermenter with the total potential extract of the grain bill. In this article, the measurement point is the fermenter; some breweries use different definitions, so always compare figures taken at the same stage.

Three terms are worth separating:

Conversion efficiency describes how effectively starch is converted into soluble extract during the mash.
Mash or pre-boil efficiency measures the proportion of grain extract recovered in the kettle before boiling.
Brewhouse efficiency also includes subsequent losses before the wort reaches the fermenter.

A mash can perform well while brewhouse efficiency remains lower because several liters of wort were left behind.

How to Calculate Brewhouse Efficiency

You need three pieces of information: the extract potential of each grain, the actual wort volume into the fermenter, and its original gravity (OG).

Step 1: Calculate Your Grain Bill’s Potential

Each malt has a maximum extract yield. For an approximate metric calculation, express it as gravity point-liters per kilogram (L°/kg). Use the malt manufacturer’s specifications when available; different grains have different potentials.

Suppose you brew with:

4.5 kg (9.9 lb) pale malt, assumed potential 300 L°/kg (about 36 PPG)
0.5 kg (1.1 lb) crystal malt, assumed potential 288 L°/kg (about 34.5 PPG)

The total theoretical potential is:

\begin{aligned} &(4.5 \times 300) + (0.5 \times 288) \\ &= 1{,}494 \text{ point-liters} \end{aligned}

These potentials are illustrative, not universal malt specifications.

Step 2: Measure the Wort You Actually Collected

After cooling and transferring, measure the volume that reached your fermenter. For this example, assume 23 L (6.1 US gal). Don’t substitute your planned batch volume if the actual amount is different.

Record your OG as well. Imagine a hydrometer reading of 1.044 SG, with the sample at the instrument’s calibration temperature or properly corrected for temperature.

To express SG as gravity points:

(1.044 - 1.000) \times 1{,}000 = 44 \text{ points}

Multiply by the volume:

44 \times 23 = 1{,}012 \text{ point-liters}

That is the approximate extract recovered in your fermenter using the common gravity-points method.

Step 3: Divide Actual Extract by Potential Extract

The calculation is:

\begin{aligned} &\text{Brewhouse efficiency (\%)} \\ &= \frac{\text{actual point-liters}}{\text{potential point-liters}} \times 100 \end{aligned}

For this batch:

\frac{1{,}012}{1{,}494} \times 100 = 67.7\%

Your brewhouse efficiency is approximately 68%. This is a practical approximation: for greater precision, especially at higher gravities, extract can also be calculated using wort density and degrees Plato.

Rather than doing this by hand every brew day, enter your grain bill, gravity, and volume into the free Brewhouse Efficiency Calculator.

Why Is My Brewhouse Efficiency Low?

One disappointing batch doesn’t automatically mean your mash technique is wrong. Work backward through the process to identify where extract was lost.

1. Grain Crush

An overly coarse crush can leave starch less accessible, reducing extract recovery. Too fine a crush, however, may cause a stuck sparge or poor flow, depending on your equipment. Aim for a consistent crush that suits your lautering system.

2. Mash Conditions

Mash temperature, time, pH, mixing, and water-to-grain ratio can affect conversion. If starch conversion is incomplete, additional sparging alone will not fully solve the problem. Check mash measurements first instead of immediately extending every brew day.

3. Lautering and Sparging

Channeling, uneven rinsing, rushed runoff, or excessive wort retained by the grain can reduce pre-boil efficiency. Measure both pre-boil volume and gravity. Those two readings help distinguish conversion or lautering problems from losses later in the process.

More sparging is not always better. Oversparging can introduce unwanted compounds and create quality problems, especially as runoff gravity falls and pH rises.

4. Kettle and Transfer Losses

Hops, trub, dead space, and transfer lines can retain wort containing extract. Highly hopped beers can show lower brewhouse efficiency even when mash performance is unchanged.

If pre-boil extraction is healthy but your efficiency into the fermenter is low, investigate those losses before changing your mash schedule.

5. Inaccurate Measurements

The most overlooked problem may be measurement rather than process. A hot sample, an uncalibrated hydrometer, poor mixing, or inaccurate kettle volume markings can distort your efficiency calculation.

Check both gravity and volume with the same method from batch to batch. Consistency in measurement matters as much as consistency in brewing.

What Is a Good Brewhouse Efficiency?

There isn’t one percentage that every brewery should target. A compact all-in-one system, a conventional three-vessel brewhouse, and a small commercial setup have different equipment losses and operating constraints.

For example, one brewer may consistently achieve 68%, while another reaches 78%. The second number is not automatically a sign of better beer or better brewing. A predictable 68% lets you formulate recipes accurately; an unpredictable 78% can still cause missed targets.

For recipe planning, use your measured average, not a default percentage borrowed from another brewer’s setup. If your actual system runs at 68%, designing every recipe for 80% is a recipe for lower-than-expected OG.

Track Your Numbers Across Several Batches

A simple brew-day log should include:

Grain weights and extract potential assumptions
Pre-boil volume and gravity
Original gravity after cooling
Cooled volume transferred into the fermenter
Notable losses to hops, trub, and equipment
Changes in crush, mash, or sparge procedure

Measure several comparable batches before revising your baseline. If the result drops suddenly, look for what changed: a new grain mill setting, a different lautering method, or an unusually large hop addition.

You can keep recipe targets together in Recipe Studio and compare your actual brew-day measurements against the plan using Batch Tracking in Foambyte™. The purpose is simple: fewer surprises and more repeatable batches.

Better Efficiency Starts With Better Measurements

Brewhouse efficiency is not a competition. It is a tool for understanding where your extract goes, building accurate recipes, and detecting changes in your process.

Start with the same measurement points every time, distinguish mash efficiency from fermenter efficiency, and make one process adjustment at a time. Small, measured improvements beat guesswork.

Want to check your latest batch? Use the free Brewhouse Efficiency Calculator and compare the result with your next brew day.