UK alcohol units explained: how many is too many?
One unit is 10ml of pure alcohol — about what your liver clears in an hour. Sounds tidy, until you learn a single large glass of wine is more than three of them.
The unit system was introduced in 1987 to give Britain a common language for how much people actually drink, and it remains the basis of every official UK guideline today. The catch is that almost nobody's mental maths matches reality: "a couple of pints" is closer to five units than two, and a bottle of wine shared over dinner is nearly a full week's guideline between two people.
This guide covers what a unit really is, the formula to count them in any drink, what the 14-units-a-week guideline looks like in actual pints and glasses, and where the UK's drink-drive limits sit.
What exactly is one unit?
One UK unit is 10 millilitres (8 grams) of pure alcohol, whatever drink it arrives in. The NHS uses it because it's roughly the amount of alcohol a healthy adult body processes in an hour — so a drink's unit count doubles as a rough guide to how long it stays with you.
The cleanest example is a single pub measure of spirits: 25ml of 40% vodka, gin or whisky is exactly one unit. Everything else scales from there — and mostly upward.
The formula: count units in any drink
You only need the volume and the strength (ABV, printed on every label):
volume (ml) × ABV % ÷ 1,000 = units
A pint of 4% lager: 568 × 4 ÷ 1,000 = 2.3 units. A large 250ml glass of 13% wine: 250 × 13 ÷ 1,000 = 3.3 units. That's the whole system.
Unit calculator
A pint is 568ml, a small wine glass 125ml, a standard 175ml, a large 250ml. Single spirit measures are 25ml (35ml in some venues, especially Northern Ireland).
Units in common drinks
| Drink | Serving | Units |
|---|---|---|
| Single spirit (40%) | 25ml | 1.0 |
| Alcopop (4%) | 275ml bottle | 1.1 |
| Lager/beer (5%) | 330ml bottle | 1.7 |
| Double spirit (40%) | 50ml | 2.0 |
| Lager (4%) | Pint (568ml) | 2.3 |
| Wine (13%) | Standard glass (175ml) | 2.3 |
| Cider (4.5%) | Pint (568ml) | 2.6 |
| Craft IPA (5.4%) | Pint (568ml) | 3.1 |
| Wine (13%) | Large glass (250ml) | 3.3 |
| Wine (13%) | Bottle (750ml) | 9.8 |
Two things stand out. Strength matters as much as size — swapping a 4% lager for a 5.4% craft IPA adds nearly a unit per pint without your glass looking any different. And wine glasses have quietly grown: order "a glass of wine" and get the large, and you're drinking a third of the weekly guideline in one pour.
The 14-units-a-week guideline
Since 2016, the UK Chief Medical Officers' guideline has been the same for men and women: to keep health risks low, drink no more than 14 units a week, spread over three or more days, with several drink-free days. Saving all 14 for Saturday doesn't count — bingeing carries its own risks even if the weekly total looks fine.
In real drinks, 14 units is roughly six pints of 4% lager, six standard glasses of 13% wine, or fourteen single spirits — for the whole week. The guideline isn't a "safe" amount; the CMOs are explicit that no level of drinking is risk-free. Fourteen units is where the added risk of alcohol-related illness stays low.
Units and the UK drink-drive limits
The limit depends on where you are. In England, Wales and Northern Ireland the legal limit is 80mg of alcohol per 100ml of blood (35µg per 100ml of breath). Scotland lowered its limit to 50mg back in 2014 — so a driver who is legal in Carlisle can be over the limit 10 minutes up the road in Gretna.
That gap may be closing: the government's 2026 road safety strategy consultation proposed cutting the England and Wales limit to 50mg to match Scotland, but as of mid-2026 the 80mg limit still applies. Don't bank on the law — bank on the safe option.
More importantly, no unit count reliably keeps you under any limit. The same two pints produce different blood alcohol levels depending on your weight, sex, food, and timing — which is why official advice is simply to avoid alcohol entirely if you're driving. If you've had a heavy night, you can still be over the limit well into the next morning.
Why counting units beats counting drinks
"I had three drinks" could mean three units or eleven, depending on whether those drinks were bottles of lager or large glasses of wine. Units cut through that. A few honest habits make the count stick:
- Log the actual serving. A large wine is 3.3 units, not "one glass". Home pours are usually bigger than pub measures.
- Check the ABV, not the category. "Beer" spans 3.4% session ales to 8% imperial stouts — the label's percentage is what counts.
- Track the week, not just the night. The guideline is weekly; a quiet Tuesday glass and a big Friday add up faster than either feels.
- Plan drink-free days. The CMOs recommend several per week — they're also the easiest way to keep the total down.
Frequently asked questions
What is one unit of alcohol in the UK?
10ml (8g) of pure alcohol — the amount in a single 25ml measure of 40% spirit, and roughly what your body processes in an hour.
How do I calculate units in a drink?
Volume in ml × ABV ÷ 1,000. A pint of 4% lager is 568 × 4 ÷ 1,000 = 2.3 units. Or use the calculator above.
How many units a week is safe?
The UK guideline is no more than 14 units a week for men and women, spread over three or more days. It's a low-risk level, not a safe one — no amount of drinking is risk-free.
How many units is a bottle of wine?
About 9.8 units for a 750ml bottle at 13% — roughly 70% of the weekly guideline.
How many units can I drink and still drive in the UK?
There's no reliable answer — alcohol affects everyone differently, and Scotland's limit is lower than England's. If you're driving, the only safe number of units is zero.