ABV Explained

ABV is an abbreviation for Alcohol By Volume and simply represents what proportion of the total volume of liquid is alcohol. To measure the ABV of a beer, a brewer will use a hydrometer, which measures the density of liquid in relation to water. The hydrometer will be calibrated to read 1.000 in water. The denser the liquid, the higher the hydrometer reading.

Before yeast is introduced to ferment beer, the brewer will take a hydrometer measurement to determine what's called the original gravity, or OG. After yeast is added fermentation begins. After the required fermentation, another hydrometer reading is taken to record the final gravity (FG). The longer the fermentation, the lower the FG and the higher the strength of the beer.

Calculating the ABV:
Say the OG measured at 1.075, and the FG 1.042. Subtract the FG from the OG and multiply by 131.

i.e. 1.075 - 1.042 = 0.033 x 131 = 4.323% ABV
Simply put, the higher the ABV, the stronger the beer. It is usually indicated at the point of dispense (on the pump clip or on the bottle). This should give you a good guide when choosing your beer at the bar or supermarket.