The easiest way is to look on the bottle and take the manufacturer's word for it.
However, it's possible to test it if you're so inclined (and have a sufficiently equipped laboratory). The easiest way would be GC/MS, which on a modern instrument will tell you which peak contains the ethanol and how much of it there was. If you know the amount of liquor introduced into the system, then you can just divide the amount of ethanol by the total sample size and multiply by 100 to get the percentage.
If you don't have a GC/MS sitting around idle (they're not expensive by lab standards, but extremely pricey by household standards ... a few thousand dollars for a cheap used one), then you're into quantitative organic chemistry, and may God have mercy on your soul.
you calculate the litres first and multiply by the alcohol percentage
Skyy vodka contains 40% alcohol.
Vodka typically contains around 40 alcohol by volume.
Rum typically contains around 40 alcohol by volume.
The total volume of the solution is 225ml + 65ml = 290ml. The percentage of alcohol in the solution is (65ml / 290ml) x 100% = 22.4%.
Red wine typically contains around 12-15 alcohol by volume.
In the United States the percentage of alcohol by volume in Miller Lite is 4.2. It contains 110 calories per bottle or can according to the Miller website.
Lager usually contains around 3% to 6% alcohol (ethanol).
A 65 proof beverage contains 32.5 percent alcohol by volume (ABV). The proof system is calculated by doubling the percentage of alcohol, so 65 proof means 65 divided by 2 equals 32.5 percent alcohol.
To determine the mass of 32.5 cm3 of alcohol, you would need to know the density of the specific type of alcohol. Once you have the density, you can multiply the volume (32.5 cm3) by the density to find the mass.
BAC stands for Blood Alcohol Concentration. It is a measurement of the amount of alcohol in a person's blood, typically expressed as a percentage. It is used to determine the level of intoxication or impairment due to alcohol consumption.
Percentage by volume (ABV) represents the amount of alcohol present in a beverage compared to the total volume. Units of alcohol are a measure used to quantify the amount of pure alcohol consumed. To calculate units of alcohol, you multiply the volume of the drink in ml by the ABV percentage and divide by 1000. This gives you the amount of pure alcohol in the drink, measured in units.