You’re standing at the bar. Maybe you’re at a wedding, or just grabbing a quick pint after a rough Tuesday. You look at your drink and wonder: how much is a unit of alcohol, anyway?
It’s a deceptively simple question.
Most people think one drink equals one unit. Honestly? That’s almost never true anymore. Not with the way craft beers have spiked in ABV or the way wine glasses have ballooned in size since the 1990s. If you’re trying to track your intake for health reasons, or maybe you’re just curious why one "large" glass of Sauvignon Blanc makes you feel significantly buzzier than a bottle of light lager, the math matters.
The concept of the "unit" was first introduced in the UK back in 1987. The goal was simple: help people keep track of their drinking using a standardized measurement. But a unit isn't a physical object you can see. It’s a measure of pure ethanol.
Specifically, one unit is defined as 10 milliliters (or about 8 grams) of pure alcohol.
Why your "one drink" is probably two
Here is the thing. A standard glass of wine at a restaurant is often 175ml or even 250ml. If that wine is a punchy Shiraz at 14% ABV, you aren't drinking one unit. You’re drinking 3.5 units. In a single glass.
It’s kind of wild when you think about it. You could be "within your limit" of two drinks but actually be three times over the recommended daily guidance because of the strength of the pour. This is where most people get tripped up. The volume of the liquid is not the same as the volume of the alcohol.
To figure out how much is a unit of alcohol in any specific drink, you have to use a bit of basic math. You take the total volume in milliliters, multiply it by the Alcohol by Volume (ABV) percentage, and then divide by 1,000.
So, let’s look at a standard 568ml pint of 4% lager.
$568 \times 4 / 1000 = 2.272$ units.
But if you swap that for a trendy 6.5% IPA?
$568 \times 6.5 / 1000 = 3.692$ units.
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Same glass. Different reality for your liver.
How much is a unit of alcohol across different drinks?
The math is annoying to do while you’re out with friends. Nobody wants to pull out a calculator at the pub. It feels clinical. It kills the vibe. But having a mental map of common drinks helps you realize how quickly those numbers stack up.
Let's look at spirits. A single shot (25ml) of 40% ABV vodka, gin, or whiskey is exactly one unit. It’s the closest thing we have to a "perfect" measurement. However, many bars now serve 35ml or 50ml measures as their default. A double gin and tonic is instantly 2.8 units if they’re using 40% spirit.
Wine is the biggest culprit for "unit creep."
A small glass (125ml) of relatively weak wine (12%) is 1.5 units.
A large glass (250ml) of strong wine (14%) is 3.5 units.
If you finish a bottle of 13% wine by yourself over dinner, you’ve just consumed 9.75 units.
The NHS and various health organizations like Drinkaware suggest that adults shouldn't regularly exceed 14 units a week. If you’re doing the math on that wine bottle, you realize that two bottles of wine a week puts you well over the "low risk" threshold. It’s a sobering realization for a lot of social drinkers who don’t consider themselves "heavy" drinkers.
The ABV trap
Alcohol by Volume is a percentage. It tells you how much of the liquid is pure ethanol. In the last decade, we’ve seen a massive shift in how drinks are produced.
Back in the day, your average session bitter or lager sat comfortably around 3.5% or 3.8%. Today, craft breweries are regularly churning out "hazy" pales and stouts that hover between 6% and 9%. The difference in units is astronomical. Drinking a 440ml can of an 8% DIPA is like drinking 3.5 units in one go. That’s more than three shots of tequila.
Does your body care about units?
Yes. Very much so.
Your liver is a remarkable organ, but it’s essentially a biological filter with a fixed processing speed. On average, a healthy adult liver can process about one unit of alcohol per hour.
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This is why "pacing yourself" is actually rooted in biology. If you drink three units in an hour, your body now has a backlog. That alcohol stays in your bloodstream, circulating to your brain and heart, while your liver frantically tries to catch up. This is what leads to intoxication. If you understand how much is a unit of alcohol, you can actually start to predict how your body will react to a night out.
If you drink five units at 9:00 PM, you won't be "clear" of that alcohol until roughly 2:00 AM.
Misconceptions that lead to hangovers
One of the biggest myths is that a "pint of cider is basically the same as a pint of beer."
Nope.
A lot of mainstream ciders are significantly stronger than standard lagers. Some apple ciders sit at 4.5%, while others—especially the fruit-flavored ones—can be much higher. A pint of 5.2% Stella Artois is 3 units. A pint of 4.5% Magners is 2.6. It sounds like a small difference, but over four pints, that’s an extra 1.6 units—nearly another two shots of vodka.
Then there's the "home pour" problem.
When you pour yourself a glass of wine at home, do you use a measuring jigger? Probably not. Research from the University of Cambridge found that people consistently pour larger servings at home than they would receive in a licensed venue. If you're filling a large balloon glass halfway, you might be pouring 200ml or more. Without realizing it, your "two glasses while watching Netflix" could actually be 6 or 7 units.
Gender and Size: The Great Equalizers
It’s worth mentioning that units don't affect everyone the same way. This isn't just about "tolerance" or being a "lightweight." It's about water content and body mass.
Alcohol is water-soluble. Men generally have a higher water-to-fat ratio than women. This means that if a man and a woman of the same weight drink the exact same number of units, the woman will likely have a higher Blood Alcohol Concentration (BAC). Her body has less water to dilute the ethanol. This is why the 14-unit weekly limit is applied to both men and women now—to simplify the message—but the physiological impact still varies wildly.
Practical steps for tracking your units
If you’re looking to cut back or just want to be more mindful, you don't need to carry a notebook. But you do need to be honest.
Check the label. By law, most bottles and cans have to list the ABV. Some even list the total units on the back. It’s a tiny icon, usually a little bottle or glass with a number inside. Look for it. It takes two seconds.
Buy smaller glasses. It sounds silly, but the "Delboeuf illusion" is real. If you use a massive glass, a 125ml pour looks like a tiny splash, making you feel deprived. If you use a smaller, traditional bistro-style glass, that same 125ml looks like a full serving.
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Alternate with "spacer" drinks. If you know you’re drinking a high-unit beverage—like a 7% IPA—follow it with a glass of water or a soda. This isn't just for hydration; it gives your liver that hour it needs to process the unit you just handed it.
Use an app. There are dozens of free unit calculators. You plug in the drink and the percentage, and it does the math. Seeing the "total units" for a week visualized in a bar chart can be a massive wake-up call for people who think they’re moderate drinkers.
Why the 14-unit limit exists
The Chief Medical Officers’ guideline of 14 units a week isn't a random number pulled out of a hat. It’s based on the point where the risk of developing serious health conditions—like cancer, liver disease, or cardiovascular issues—starts to climb significantly.
Drinking 14 units spread over three days is very different from drinking 14 units on a Saturday night. Binge drinking (defined as more than 6 units for women or 8 units for men in one session) causes acute stress to the system that a steady, low-level intake doesn't.
Understanding how much is a unit of alcohol gives you the agency to make choices. It’s not about being "anti-alcohol." It’s about knowing that your craft beer habit might be delivering more ethanol to your system than you bargained for.
The Takeaway
Next time you’re looking at a drink menu, do a quick mental check.
Is it a pint or a bottle?
Is the ABV 4% or 6%?
Is that "single" actually a double?
Knowing the unit count is the only way to accurately gauge your relationship with alcohol. It moves the conversation away from "I feel fine" to "I know exactly what I’m putting into my body."
What to do next:
- Look at the bottle of whatever you have in your fridge right now. Find the ABV.
- Use the formula: (Total ml x ABV) / 1,000.
- Determine if that "one drink" is actually the amount of alcohol you intended to have.
- If you're consistently over 14 units a week, try swapping one high-ABV drink for a lower-strength alternative or a 0.0% version. The taste gap has narrowed significantly in recent years, but the health benefits are immediate.
Disclaimer: This information is for educational purposes and reflects general health guidelines. If you are concerned about your alcohol consumption or its impact on your health, please consult a medical professional or a specialized support service.