It is very simple to calculate the alcohol percentage of your brew by using your hydrometer.
All you need to do is take your Starting S.G. (specific gravity) & Final S.G. and calculate it according to the below formula:
Start S.G. – Final S.G. = (XXXX)
(XXXX) Divided by 7.36 = % Alc. Vol.
Add 0.5% to allow for alcohol produced from the priming sugar and you will have your overall % Alc. Vol.
Ie: 1038 – 1006 = 32
32 divided by 7.36 = 4.35 %
4.35% + .5% = 4.85% (Alc. Vol.)
If you keg your beer and gas it using Co2, don’t add the .5% as no further alcohol is produced.