Ok then what formula would you use to calculate Conversion efficiency?

Here's how you calculate conversion efficiency (the equations you actually need to use are in

**bold blue**.)

Conversion efficiency is defined as:

Conversion Efficiency = Wt of Extract Created in Mash / Max Potential Extract Wt

Max Potential Extract Wt is calculated as shown in

post #9 in this thread:

Max Extract Wt = Weighted Ave % Extract Potential [FGDB] * (1 - Weighted Ave % Moisture) * Total Grain Bill Wt

SG in °Plato is defined as Weight% extract in the wort, and is given by:

°P = 100°P * Extract Wt / (Extract Wt + Water Wt)

The maximum SG the wort in the mash can achieve is:

Max Wort °P = 100°P * Max Extract Wt / (Max Extract Wt + Strike Water Wt)

And the SG actually achieved in the mash is:

Actual Wort °P = 100°P * Actual Extract Wt / (Actual Extract Wt + Strike Water Wt)

We can solve the above formula for SG for Actual Extract Wt. if we know the SG:

Actual Wort °P * (Actual Extract Wt + Strike Water Wt) = 100°P * Actual Extract Wt

Actual Wort °P * Actual Extract Wt + Actual Wort °P * Strike Water Wt = 100°P * Actual Extract Wt

Actual Wort °P * Strike Water Wt = 100°P * Actual Extract Wt - Actual Wort °P * Actual Extract Wt

Actual Wort °P * Strike Water Wt = (100°P - Actual Wort °P) * Actual Extract Wt

Actual Extract Wt = Actual Wort °P * Strike Water Wt / (100°P - Actual Wort °P)

We can now substitute the formulas for Actual Extract Wt and Max Extract Wt into the formula for Conversion Efficiency:

Conversion Efficiency = (Actual Wort °P * Strike Water Wt / (100°P - Actual Wort °P)) / (Weighted Ave % Extract Potential [FGDB] * (1 - Weighted Ave % Moisture) * Total Grain Bill Wt)

or, to get it all on one line:

**Conv Eff = (Wort °P * Strike Wt / (100°P - Wort °P)) / (% Extract Potential * (1 - % Moisture) * Grain Bill Wt)**

The above formula uses two things most homebrewers don't deal with: SG in °Plato, and water weight. A couple of formulas can convert from water volume to water weight, and °P to SG in "normal" form (i.e. Density of Wort / Density of Water = 1.0xx.)

Water weight is just Water Volume * Water Density, where both values are measured (or corrected to) the same temperature. At 68°F (20°C) water has a density of 8.3304 lb/gal or 0.9982 Kg/L. So, calculate your strike water weight as:

**Weight in lb = Volume in gal * 8.3304 lb/gal**

**Weight in Kg = Volume in L * 0.9982 Kg/L**

The usual equation for converting SG to °P is:

**°Plato = (-1*616.868)+(1111.14*SG)-(630.272*SG^2)+(135.9975*SG^3)**

You can copy the above formula directly into a spreadsheet, and replace "SG" with the cell address containing the SG value.

Another potential issue is having grain potentials only in SG format (1.0xx). Table sugar (sucrose) is the reference for 100% potential, as 100% of the material goes into solution. In SG format sucrose has a potential of 1.0462. To convert a potential in SG to % use:

**Potential % = 100% * (Potential SG -1) / 0.0462** (or ppg / 46.2)

Brew on