Sugar addition by Calculation
Fall Bright, The Winemakers Shoppe

First:  Take a hydrometer reading of the fresh juice.  Then use the technique below to determine the amount of sugar to add to raise the brix to the desired level.  

The rates given in the chart on the previous page are subject to rounding off to the nearest tenth.  The rates are for pounds to add to 1 gallon.

Fact:   .125 pounds of sugar will raise 1 gallon 1 brix or degree.   
One ounce is .0625 pounds.  
One pound of corn (dextrose) sugar is 3 cups and
approximately 1 pound of table (sucrose) sugar is 2 ¼ cups.   
Honey:   5 pounds of honey is equivalent to 4 pounds of cane sugar.    

General conversion of sugar to alcohol is approximately 58% (0.575%~).

To calculate sugar adjustment to 21 brix using straight math: