How to Calculate a Unit of Alcohol

We’re given rough guidelines about what one unit of alcohol represents. However, different drinks have different strengths, so guidelines can be misleading. Here’s how to calculate how many units your favorite tipple contains.

With Christmas just around the corner, and the celebrations kicking off, it’s good to be informed about what you’re drinking and how much you can handle, because sometimes the consequences can be dire. It doesn’t matter whether you drink wine, beer or liquor, a unit of alcohol is a unit of alcohol.

The bottom line is that one unit of pure alcohol equals 8 grams. This is a bit confusing because alcohol is a liquid and is measured in either milliliters or fluid ounces, and grams are a measure of weight. So how on earth can we work it out? It depends to some extent on where you live.


In Europe liquids are measured in milliliters. Now, I could confuse you, and myself, with science, but I won’t. There’s a simple formula:

Volume X Percent/1000 = Units of Alcohol

In other words, if you have a big glass of red wine which measures 175 ml, and the label on the bottle tells you that the wine is 13.5% Alcohol by Volume, you multiply 175 by 13.5 and then divide the result by 1000, giving you a grand total of 2.35 units. Surprised?


In the USA, liquids are measured in fluid ounces. It’s also worth noting that the alcohol content is sometimes expressed as “Proof”. The percent of alcohol by volume can be obtained by dividing the proof amount by 2. So if a drink is 80 proof, you can calculate that it is 40% Alcohol by Volume. The formula to convert US Fluid Ounces to Units of Alcohol is:

Volume X Percent/33.8 = Units of Alcohol

Take, for example, a small shot (1.25 fluid ounces) of 80-proof vodka. You must first divide 80 by 2 to arrive at 40% Alcohol by Volume. Then you multiply 1.25 by 40 and divide the result by 33.8, giving you a total of 1.48, or just under 1.5 units.

Be Wary

The alcohol content of your favorite tipple can vary widely. Wines can be as low as 7% and as high as 13.5% alcohol. If you order a glass of house wine in a pub or restaurant, you won’t be aware of the alcohol content unless you get the opportunity to look at the label on the bottle.

Lagers, on average, are about 5% but can go as high as 8.5%, spirits average 40%, Alco pops are around 4-5%, ciders are 4-7%, and bitters are 4.5-6.5% generally. The biggest range is for liquors and spirits, which can be as low as 17% and as high as 40%. So it does pay to be aware of what you’re drinking.


The average liver can process 1 unit of alcohol per hour, that’s all!

Have a happy and safe Holiday season!

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  1. Interesting and well researched article.

  2. It’s clear that you’ve put a lot of work into this. I’m not a drinker, but at least now I know how all this works.

  3. Great information, Dee. Wonderful job!

  4. Useful tips, for now I’ll stick to the designated driver. Although don’t the affects differ on differently weighted people? Not like who can handle more, but the affect the BAC has on the blood of a bigger person.

  5. You’re right, Jared, weight and age make a difference, but I thought it would be too complicated to go into here. This is an easy-to-calculate formula that provides better accuracy than official guidelines which are based on a simple average.

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