How Many Units Is That Drink? The Answer Has Changed

The phrase “a glass of wine” has stopped carrying useful information. It can mean 1.6 units or 3.25 units depending on the glass, and the same bottle can yield three servings or six.

The formula itself is simple. What has drifted is everything the words used to imply.

The formula

UK units = volume in litres × ABV percentage

That is clean because of how a unit is defined. One UK unit is 10 ml of pure alcohol, weighing about 8 g. A litre of a 1% drink contains 10 ml of alcohol, so litres times percentage gives units directly.

Worked examples:

• 175 ml of 13% wine: 0.175 × 13 = 2.3 units
• 750 ml bottle of 13% wine: 0.75 × 13 = 9.75 units
• Pint of 5.2% lager: 0.568 × 5.2 = 2.95 units
• 25 ml single of 40% spirit: 0.025 × 40 = exactly 1 unit

That last one is where the whole system started, and it is why the single measure remains the easiest unit to reason about.

Two things have drifted

Glasses got bigger. A large glass is now commonly 250 ml, which was an unusual pour thirty years ago. At 250 ml of 13% wine you are drinking 3.25 units in one glass, more than three single spirits.

Wine got stronger. Typical table wine has moved from around 11% to 13% or 14% over a few decades, driven by warmer growing conditions and by a preference for riper fruit. Some New World reds sit at 15%.

Combined, a “glass of wine” poured today can carry roughly twice the alcohol of one poured in the 1990s, using identical language.

Home pours make it worse. Studies of self-poured drinks consistently find people pour substantially more than a measured serving, particularly into wide-bowled glasses, and consistently underestimate what they poured. Most people are pouring a bottle into three glasses while believing they are pouring four.

Units are not international

This causes genuine confusion when reading health guidance from other countries.

• United Kingdom: 1 unit = 8 g of alcohol
• Australia, much of Europe: 1 standard drink = 10 g
• United States, Canada: 1 standard drink = 14 g
• Japan: 1 unit = about 20 g

So the US guidance of “up to two drinks a day” is about 3.5 UK units a day, or 24.5 a week, well above the UK figure of 14.

The countries disagree less than the raw numbers suggest, but they are also not saying the same thing. Comparing the figures without converting first produces nonsense in both directions.

What the guidelines say now

The UK Chief Medical Officers advise no more than 14 units a week for everyone, spread over three or more days, with several drink-free days.

Fourteen units is about six pints of 4% beer, or a bottle and a half of wine. Not a week’s worth for many people, which is rather the point of publishing it.

The spreading matters as much as the total. Fourteen units in one evening carries very different risks from fourteen across a week. Acute risks, including injury, accidents and alcohol poisoning, scale with session size. Chronic risks, including liver disease and several cancers, scale more with the cumulative total.

Guidance has moved consistently downward over the past decade. Canada’s 2023 revision was dramatic, replacing a weekly limit with advice that risk begins increasing above about two standard drinks a week.

The health claims that collapsed

For years the accepted position was that moderate drinking, especially red wine, protected the heart. That claim has largely fallen apart, and the reason is worth understanding because the same flaw appears elsewhere.

The problem was the comparison group. Studies compared drinkers against non-drinkers, but non-drinkers include people who stopped because they were already ill, and people who never drank for reasons correlated with other health factors. This makes abstainers look unhealthier than they are, and moderate drinkers look healthier by contrast.

Studies using Mendelian randomisation, which compares people by genetic variants affecting alcohol metabolism rather than by self-reported behaviour, and which is therefore far harder to confound, generally find no protective effect at any level.

The WHO position since 2023 is that no level of alcohol consumption is safe for health.

This does not mean a drink is dangerous. It means the risk curve starts at zero and rises, rather than dipping first. The honest framing is that drinking is a trade you make knowingly, not a health measure.

The calories nobody counts

Alcohol carries 7 calories per gram, closer to fat at 9 than to carbohydrate or protein at 4, and it arrives with no nutritional value whatsoever.

• Large glass of wine: roughly 200 calories
• Pint of lager: around 220
• Bottle of wine: around 600

Six pints across a weekend is about 1,300 calories, most of a day’s intake, and almost nobody logs it when tracking food.

Alcohol also suppresses fat oxidation while it is being metabolised, because the body prioritises clearing it over everything else. So the calories behave slightly worse than the number alone implies.

Clearing it takes as long as it takes

An average adult clears roughly one unit an hour, varying with body size, sex, food and liver function.

Ten units finishing at midnight means alcohol is still present well into the following morning. This is the mechanism behind most morning-after driving offences, and people are genuinely surprised by it.

Nothing accelerates the process. Coffee, a cold shower, fresh air and exercise all change how alert you feel while leaving your blood alcohol exactly where it was. That combination, feeling sober while being over the limit, is considerably more dangerous than simply feeling drunk.

The useful habit

Work out the units in what you actually drink, in the glass you actually use, once. Most people are surprised by a factor of roughly two.

After that you do not need to calculate anything again. You just know that your usual glass is 3 units rather than 1, and that changes what a normal week looks like without requiring any further arithmetic.