Apologies up front if there is already a thread addressing this, but I can't find it if there is. What formula can I use to calculate ABV in my home brews? The Joy of Home Brewing provides the following formula:

(OSG-FSG)105

For purposes of comparison, lets let OSG = 1.080 and FSG = 1.020

This formula yields a ABV of 6.3%

Another formula I've run across is:

((OSG-FSG)1.05)/FSG/.79

This formula yields an ABV of 7.8%

That seems like a pretty large difference between two formulas that are supposed to be calculating the same thing. Is there any consensus out there about a good formula to use (that does not require an advanced degree in mathematics)?