To calculate alcohol units, multiply the volume of your drink in milliliters by its ABV (alcohol by volume) percentage, then divide by 1,000. A single unit equals 10ml or 8g of pure alcohol. This simple formula works for any drink, from a light beer to a strong cocktail, as long as you know the serving size and the ABV printed on the label.
The Formula
The calculation is straightforward:
Units = (volume in ml × ABV%) ÷ 1,000
Say you’re drinking a 330ml bottle of beer at 5% ABV. That’s 330 × 5 = 1,650, divided by 1,000 = 1.65 units. A 750ml bottle of 13% wine works out to 750 × 13 ÷ 1,000 = 9.75 units. Once you memorize this formula, you can calculate units for anything with an ABV on the label.
The ABV percentage tells you what proportion of the liquid is pure alcohol. A drink labeled 40% ABV is 40% alcohol by volume. The formula simply extracts that proportion from the total volume and converts it into standardized units.
Units in Common Drinks
Wine
Wine is where unit counts catch people off guard, because glass sizes vary widely and ABV has crept up over the years. For a typical 13% ABV wine:
- Small glass (125ml): 1.6 units
- Standard glass (175ml): 2.3 units
- Large glass (250ml): 3.3 units
A large glass of wine is a third of a bottle and contains more than three units on its own. Two large glasses and you’ve nearly finished the bottle at 6.6 units. If your wine is 14% or 15% ABV, which is increasingly common for reds, those numbers climb further. You can run the formula yourself: 250 × 14 ÷ 1,000 = 3.5 units for a large glass of 14% wine.
Beer, Lager, and Cider
A standard pint in the UK is 568ml. For a 4% lager, that’s 568 × 4 ÷ 1,000 = 2.3 units per pint. Bump the ABV to 5% and the same pint becomes 2.8 units. Craft beers often sit between 5% and 8%, so a single pint of a 6.5% IPA delivers 3.7 units.
Bottled and canned beers vary in size. A 330ml bottle of 5% beer is 1.65 units. A 440ml can of the same beer is 2.2 units. A 500ml can of 4.5% cider comes to 2.25 units. Always check both the volume and the ABV, because two beers that look similar on the shelf can differ by a full unit or more.
Spirits
A standard single measure of spirits in the UK is 25ml. For a 40% ABV spirit like vodka, gin, or whisky, that’s 25 × 40 ÷ 1,000 = 1 unit exactly. A double (50ml) is 2 units. Some bars pour 35ml singles, which comes to 1.4 units.
The spirit itself is simple to calculate, but mixers don’t change the unit count, only the total volume of liquid in your glass. A gin and tonic with a single 25ml measure of gin is still 1 unit regardless of how much tonic you add. Cocktails are trickier because they often contain multiple spirits. A drink made with 50ml of vodka and 25ml of a 20% liqueur would be 2 units from the vodka plus 0.5 from the liqueur, totaling 2.5 units.
Why the ABV on the Label Matters
The formula only works if you use the actual ABV of what you’re drinking. People often assume all wine is roughly the same strength or that beer is always around 4 or 5 percent, but the range is wide. A light lager might be 3.4%, while a barley wine or imperial stout can hit 10% or 12%. Similarly, wine ranges from about 5.5% for a Moscato to 15% or more for some Zinfandels and Shiraz.
Home-poured drinks add another layer of uncertainty. A “glass of wine” at home is rarely 175ml. Most people pour closer to 250ml without realizing it. If you’re trying to track your intake accurately, it helps to measure once with a kitchen measuring jug so you know what your normal pour actually looks like.
How Your Body Processes Units
The average adult metabolizes alcohol at a rate of about 7 grams per hour, which works out to roughly one unit per hour. This rate is relatively fixed. Coffee, food, water, and cold showers don’t speed it up. If you drink 9 units over an evening, your body needs approximately 9 hours to clear the alcohol completely.
That processing rate matters most the morning after. If you finish your last drink at midnight having consumed 10 units across the evening, your body won’t finish processing that alcohol until around 10 a.m. the next day. This is why people can still be over the legal driving limit the morning after a night out, even if they feel fine.
The rate does vary from person to person. Body weight, liver health, sex, age, and genetics all play a role. A 70kg person processes between 170 and 240 grams of alcohol per day at maximum capacity, which works out to a range of roughly 7 to 10 grams per hour. But using one unit per hour as a baseline is a reasonable estimate for most adults.
Tools That Do the Math for You
If you’d rather not run the formula each time, several free tools can help. The NIAAA (National Institute on Alcohol Abuse and Alcoholism) offers a set of online calculators including a Drink Size Calculator and a Cocktail Content Calculator, both useful for figuring out what’s actually in your glass. They also provide a Blood Alcohol Concentration Calculator and an Alcohol Consumption Tracker for logging your intake over time.
Many drink-tracking apps let you scan a barcode or select a drink from a database and will calculate units automatically. The key information you need for any of these tools is the same: how much liquid and what percentage ABV. If you know those two numbers, you can always fall back on the formula: volume in ml, times ABV, divided by 1,000.