Most of us have a rough sense that “a drink” is a unit, but the maths is less obvious than it seems. This guide explains how units work, what the NHS guidance looks like in a pub or at a dinner table, and how to cut back in ways that fit real life.
What exactly is an alcohol unit?
According to the NHS, one unit equals 10ml or 8g of pure alcohol, which is around the amount the average adult can process in an hour. The NHS adds that within an hour there should, in theory, be little or no alcohol left in the blood of an adult from a single unit, though this varies between individuals.
That “one unit an hour” idea is a useful mental model but not a safety rule. It does not account for differences in body size, medication, health conditions or how quickly someone drinks, and it says nothing about the longer-term effects of regular drinking.
How do you work out the units in a drink?
The NHS gives a simple formula: strength (ABV) multiplied by volume in millilitres, divided by 1,000, equals units. ABV is the percentage of alcohol by volume printed on the label.
A worked example: a 175ml glass of 12% wine is 12 × 175 = 2,100, divided by 1,000, which gives 2.1 units. A pint of beer is about 568ml, so at 5.2% it works out at roughly 2.95, in line with the NHS figure of 3 units.
The NHS gives these examples for common drinks:
| Drink | Units (NHS) |
|---|---|
| Single spirit measure (25ml, 40% ABV) | 1 |
| Small glass of wine (125ml, 12% ABV) | 1.5 |
| Pint of lower-strength beer (3.6% ABV) | 2 |
| Standard glass of wine (175ml, 12% ABV) | 2.1 |
| Pint of higher-strength beer (5.2% ABV) | 3 |
Two things catch people out. Home pours are often bigger than pub measures, and many wines and craft beers are stronger than the “average” used in rough guides. The label and the formula are more reliable than guesswork.
What does 14 units a week look like?
The NHS advises that men and women should not drink more than 14 units a week on a regular basis. It describes 14 units as equivalent to 6 pints of average-strength beer or 10 small glasses of lower-strength wine.
Using the table above, illustrative arithmetic shows how quickly this adds up with larger glasses. At 2.1 units per standard glass of wine, 14 units is reached after about 6.7 glasses (14 ÷ 2.1), so seven standard glasses in a week already takes you slightly over. Two pints of higher-strength beer on three evenings is 2 × 3 × 3 = 18 units, already above the guidance.
The NHS also says that if you regularly drink as much as 14 units a week, it is best to spread this over 3 or more days, and to try to have several drink-free days each week. Saving the whole allowance for one evening is not what the guidance intends.
Why is the guidance set where it is?
The NHS says that drinking more than 14 units a week over many years increases the risk of several conditions, including mouth, throat and breast cancer, stroke, heart disease, liver disease and brain damage that may cause memory loss and changes in behaviour. It also notes that heavy drinking is linked to worsening mental health and self-harm.
These are population-level associations. They describe how risk shifts across large groups of people, not what will happen to any one person. The guidance is a threshold for lower risk rather than a promise of safety below it, and it does not suggest that staying under 14 units protects anyone from these conditions.
Is a heavy night different from a heavy week?
Yes. The NHS defines binge drinking as more than 8 units in a single session for men, or more than 6 units in a single session for women. Three standard glasses of 12% wine come to 3 × 2.1 = 6.3 units, so the lower threshold is passed in a single evening more easily than many people assume.
This is why spreading drinking across the week matters in the guidance, and why a week that looks modest on paper can still include a heavy session. Total units and the pattern of drinking both count, and a week with one very large evening is not the same as the same total spread across several days.
It also helps to keep a rough tally for a fortnight. Writing down what you drank, the size of the glass and the strength is often enough to show where the units are really coming from, whether that is the weekday glass at home, a larger pour at weekends or a stronger beer than you had realised.
What are the benefits of drinking less?
The NHS lists a mix of short-term and longer-term benefits of cutting down. In the short term it mentions feeling better in the mornings, being less tired during the day, feeling more energetic, better-looking skin and easier weight management. Longer term, it points to a lower risk of cancer, diabetes, dementia, stroke, and heart, liver and kidney problems, along with improved mood and better sleep quality.
Sleep is a good place to start noticing a difference, and our piece on why sleep matters for everyday health covers the wider picture. The NHS list is a statement of potential benefits rather than a guarantee, and individual experiences vary.
Which practical changes actually help?
The NHS suggests a handful of straightforward approaches to cutting down:
- Make a plan. Decide in advance how much you are going to drink.
- Set a budget. Take only a fixed amount of money to spend on alcohol.
- Let others know. Telling friends and family makes support easier.
- Take it a day at a time. Cut back a little each day.
- Make it a smaller one. Choose smaller serving sizes.
- Have a lower-strength drink. Swap for something with a lower ABV.
- Eat first and stay hydrated. Have food and water, and alternate with non-alcoholic drinks.
- Take a break. Have several drink-free days each week.
These work best when they become routine rather than tests of willpower. Our article on how to build a habit that sticks explains why tying a change to a regular cue, such as swapping the midweek glass for a longer walk or a hot drink, tends to hold up better than relying on motivation. Food matters too, and what a balanced everyday diet looks like is a good companion read.
If drinking is tied to stress or low mood, the NHS-backed five ways to wellbeing framework offers other routes to unwinding that do not involve a glass.
When should you speak to a GP or call for help?
The NHS suggests considering support if you often feel the need to have a drink, if others warn you about your drinking, or if you suspect it is causing difficulties. A GP is a sensible first step, and the NHS advises being accurate and honest about how much you drink and any problems it causes. A GP can suggest assessments and local community alcohol services.
Take particular care if you drink heavily and regularly. The NHS lists anxiety after waking, sweating and mild tremors, and nausea or retching in the morning as symptoms that need medical attention. Hallucinations, severe tremors, and seizures or fits are emergencies: call 999. Do not stop heavy, long-term drinking suddenly without medical advice, because withdrawal can be dangerous.
For confidential advice, the NHS lists Drinkline on 0300 123 1110 (weekdays 9am to 8pm, weekends 11am to 4pm), and self-help or mutual aid groups such as Alcoholics Anonymous and SMART Recovery.
A realistic way to think about it
Units are a measuring tool, not a moral scorecard. Knowing that a large glass of wine is closer to three units than one, that 14 units is a ceiling on regular drinking rather than a target, and that several drink-free days each week are part of the guidance gives you enough to make informed choices. If you are curious where you stand more broadly, an NHS Health Check is a useful moment to talk it through, if you are eligible.
Small, specific changes such as smaller glasses, a plan and a few fixed alcohol-free evenings are usually easier to keep up than dramatic resolutions.
This article is general information, not a substitute for advice from a doctor or other qualified health professional. If you are worried about your drinking, speak to your GP or call NHS 111. If you are struggling emotionally, the Samaritans are available on 116 123.
Sources: NHS
