# OG calculation

#### Mike J

##### New Member
I want to better understand the calculation of this value.
My recipes all show a much higher OG expectation compared to my actual numbers...
Could someone point me to any documentation ?

Typically it is a function of your brewhouse efficiency setting. I usually set mine to 75%, which gives me fairly accurate numbers. Try that and see what happens.

This is a simplified explanation based on Palmer's How To Brew:

To understand (calculate OG), first calculate your "potential" gravity points (PGP).
As an example, let's say I'm making a simple 5-gallon batch of Stout with the following grain bill:
8 lbs. Pale Malt (1.036 potential = 36 gravity points)
1 lb. Roasted Barley (1.025 potential = 25 gravity points)

PGP = Grain Gravity Points * Weight / Volume
PGP = (8*36) + (1*25) / 5
PGP = 62.6 (which, in gravity looks like 1.063)
This is only a "Potential Gravity" that is impossible to actually hit on Brew Day

----------------------------------------------------------------

Expected Original Gravity (OG) = PGP (points) * Brewhouse Efficiency %
...where Brewhouse Efficiency is based on our average measured BE over all previous brews. This could be anywhere from 65-85% or even outside that range.

From the example above, using my BE:
Expected OG = 62.6 * 72% (.72)
Expected OG = 45.1 = 1.045

---------------------------------------------------------------

Now, let's say after brew day, I measure my OG as 1.048. To calculate my Brewhouse Efficiency for this batch it would be:
Efficiency = Actual OG Measured in Points / Potential Gravity Points
Efficiency = 48/62.6
Efficiency = 77% for this Brew Day (this can be used as another efficiency data point when calculating Expected OG for future brews.)

The key to the whole thing is to understand your efficiency, which comes with taking good notes, brewing batch after batch, and dialing in your system

I should note that "Brewhouse Efficiency" as described in my post above is not the same as the Brew House Efficiency calculated in the software on Brewer's Friend. I probably should have called it something else.

Thankyou all, lots to think about

I should note that "Brewhouse Efficiency" as described in my post above is not the same as the Brew House Efficiency calculated in the software on Brewer's Friend. I probably should have called it something else.
hi, good detail on the calculations, it does help.
Actually, I was asking about the Efficiency calculated in the software,

This doc helped me understand the various brewing efficiencies.

This doc helped me understand the various brewing efficiencies.
Great explanation in that article. I'm a little embarrassed I didn't look deep enough into our own documentation to find it...
Many thanks

Great explanation in that article. I'm a little embarrassed I didn't look deep enough into our own documentation to find it...
Many thanks
At some point I'll go through and update these and make links in the relevant sections of the recipe builder and brew session pages...

If you remember any further questions you had as you read through it, we'd really appreciate the feedback so we can continue to improve!

At the homebrew level, efficiency is trial and error. Mine is God awful with the bag, but I know it is and add more grain. I took different recipes and compared results to estimates and adjusted from there.

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