Scales for Measuring Alcohol Strength
There are three scales of measuring proof namely:
- Gay Lussac or GL system: In this system, the proof is equal to the percentage of alcohol in the spirit. So if Vodka has 43% alcohol it is 43⁰ proof GL.
- British or Canadian Proof: Bartholomew Sykes devised a hydrometer which calculated that 57.1⁰ % of alcohol is equivalent to 100⁰ % BP. So 100% of alcohol is equal to 175 ⁰ BP.
- American or US Proof: In this system, 50% alcohol is equal to 100⁰ US proof. Therefore 100 % alcohol is equal to 200⁰ US.
Therefore we can say that : 100⁰ GL = 175⁰ BP = 200⁰ US
Organization International Metrologique Legale (OIML)
It is now mandatory for all manufacturers to indicate in % the amount of alcohol on the bottle. OIML is the same as GL, which is the most logical of the systems.