In order to obtain an accurate alcohol content one must use a hydrometer before fermentation and after fermentation. The hydrometer measures the density of the liquid by floating at a given level corresponding to the specific gravity of the fluid being measured. It should be read by noting the level at which the surface of the fluid contacts the glass when the hydrometer is floating in the liquid. The first reading should be taken before the addition of yeast, and at 60 degrees F. The second reading should be taken after fermentation is complete, that is, before bottling, and before adding priming sugar. The following is a sample for determining both alcohol by weight (a.b.w.) and alcohol by volume (a.b.v.).

Your first reading (original gravity [O.G.]) = 1.045

Your second reading (final or finishing gravity) = 1.010

Subtract final from original. 1.045 - 1.010 = 0.035

multiply this figure by 105. 0.035 x 105 = 3.68% a.b.w.

Therefore, you have a brew of 3.68% alcohol by weight.

To get Alcohol by volume simply multiply your figure for % a.b.w. by 1.25

3.69 x 1.25 = 4.6% a.b.v.