You need to use your hydrometer to measure the specific gravity of your beer while you are making it. You will need two readings.(See 1 & 2 below).


After entering your two readings at left:

Click on the submit button and the percentage of alcohol will appear in red at the top,

Entering your two readings:
It doesn't matter whether you enter them as the full SG readings with the decimal point like (e.g. 1.045) or merely enter the last two digits (e.g. 45) it will calculate the percentage of alcohol for you when you click on the submit button.

NOTE: The calculated alcohol percentage includes an allowance for the alcohol made in the bottle during secondary fermentation
The first reading is of the beer wort (this is the liquid in your fermenter) before you start the fermentation. You should take this reading when all the water has been added to the wort and you are ready to add the yeast. Run a sample out of the tap into your test flask and set it aside for a while to cool to about 20C. This reading is called the ORIGINAL GRAVITY
The second reading is of the finished beer. This is taken when you are ready to bottle your beer. this readin is called the FINAL GRAVITY.