How do you determine efficiency?

I'm going to be starting my first partial mash today or tomorrow and I just realized that I have no idea how to determine what efficiency I end up with. Is it just based on what ending OG you get vs the fermentables? Is this something best suited for using one of those applications like pro mash or whatever?

Efficiency of a partial mash is really based on the gravity and volume of the wort you derive from the grain. Don't wait until after you add malt extract to measure these things.

Measure your water at every step.
Measure your grain bill.
Take hydro samples after sparging.

You'll have to know the efficiency of the grains and add it up. This will tell you what the maximum amount of sugar you could possibly extract will be. Compare your hydro reading to the maximum potential and this determines your efficiency.

You could never extract maximum sugars and even if you got very close, your wort would likely be unsuitable for brewing due to tannins and stuff. But many get over 75% and some into 80s after tweaking their process.

here is my calc for eff for one of my brews:


brew efficiency overview

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SMaTH Brewed 12-17-08 kegged 1-19-08

12# vienna
1 oz Centennial (8.00% AA 60 min)
2 oz Cascade (5-6?% AA 1 oz 30 min, 1 oz 5 min )

Mash 154*F, 4.5 gal, 1 hour
Sparge 180*F, 4 gal

Boil volume: 7-7.5 gal
Boil 1 hour
End volume: 5.5 gal

SG: 1.034
OG: 1.060
FG: 1.014

I calculate ABV: 6.03%

So here are my thoughts. The beer is great very clear, yeasty and citrusy. Has turned out to be a great people pleaser. All grain is as easy as you want it to be but I am interested in the actual efficiency of my system in order to get better data for online brew calculators.

12# Vienna
F. gravity 1.060

GU = (Grav-1)x1000
GU = 60 GU

GU of total gravity = 60 GU*5.5 gal = 330 total GU
12 # Vienna = 330 GU

total grav of wort = (SG-1)*1000 * boil volume
= 34 GU * 7 Gal (pre boil) = 238

Eff = total gravity of wort/total potential gravity of grains
Eff = 238/330 = 72%

Easy - Beersmith.

Some good information here: How to Brew - By John Palmer - Extract Efficiency and Typical Yield