How Many Units Can You Drive On – UK Drink Drive Limits Explained

The question of how many units of alcohol you can drink and still legally drive in the UK is one of the most misunderstood areas of road safety. Unlike a speed limit, which applies uniformly to every driver, the legal alcohol limit is measured in the amount of alcohol present in your breath, blood, or urine. It is not expressed in pints, glasses of wine, or units. And it varies from person to person.

Official sources including the UK government and the charity Drinkaware are explicit: it is impossible to say exactly how many drinks will put someone over the legal limit. Factors such as weight, sex, age, metabolism, food intake, and the type and strength of the drink all play a role. The safest practical takeaway, particularly in Scotland where the limit is stricter, is that even one drink can leave you over the legal threshold.

This article explains the legal limits in each part of the UK, provides rough guidance on what those limits mean in terms of common drinks, and clarifies why there is no universal “safe number” of units for driving. All figures are drawn from official government sources, medical authorities, and established road safety organisations.

How many units can you drive on in the UK?

The legal limit for driving in England, Wales and Northern Ireland is 80 milligrams of alcohol per 100 millilitres of blood. In Scotland, the limit is lower: 50 milligrams per 100 millilitres of blood. These limits are not expressed in units, but rough equivalents can be estimated. The table below provides a quick-reference summary for the four nations.

Key insights to understand before you drive after drinking:

• There is no universal safe number of units – it varies by sex, weight, metabolism, and time since drinking.
• Scotland’s limit is significantly stricter (50mg blood) compared to England, Wales, and Northern Ireland (80mg).
• Approximate unit equivalents: 1 pint of 4% lager = 2.3 units; a 175ml glass of wine (12%) = 2.1 units.
• The “four units for men, three for women” is a rough guide, not a guarantee of being under the legal limit.
• Breathalyzer limits differ: 35 micrograms per 100ml breath in England and Wales, 22 in Scotland.
• Even below the legal limit, driving skills can be impaired – best practice is zero alcohol.

As the UK government states, there are strict alcohol limits for drivers, but it is impossible to say exactly how many drinks this equals because it is different for each person. The Drinkaware charity reinforces this point, noting that the limits in England, Wales and Northern Ireland are 80 milligrams of alcohol per 100 millilitres of blood and 35 micrograms per 100 millilitres of breath. For information about renewing your licence, see our guide on Driving Licence Renewal Online.

What is the drink drive limit in Scotland compared to England and Wales?

The most significant regional difference in UK drink driving law is between Scotland and the rest of the country. Scotland lowered its limit in 2014, adopting a more stringent threshold that is now also shared by Northern Ireland as of 2021. This means there are effectively two legal standards in operation across the UK.

Scotland’s lower limit

The Scottish legal limit is 22 microgrammes of alcohol per 100 ml of breath, 50 mg per 100 ml of blood, or 67 mg per 100 ml of urine. These figures come directly from the Scottish government’s official advice website, mygov.scot. The same source emphasises that there is no reliable way to convert the drink-drive limit into a fixed number of units, pints, or glasses of wine because the legal limit is based on alcohol in your breath, blood, or urine, and it varies from person to person.

The limit in England, Wales and Northern Ireland

By contrast, the rest of the UK uses higher limits: 35 mcg/100 ml breath, 80 mg/100 ml blood, and 107 mg/100 ml urine. This means that a driver who is legal in England could be over the limit in Scotland after consuming exactly the same amount of alcohol. Drivers crossing the border need to be aware that the rules change.

How can you calculate if you are over the drink drive limit?

There is no reliable calculator that can tell you with certainty whether you are under the legal limit based on the number of drinks you have consumed. However, you can use a rough risk guide combined with an understanding of alcohol units to estimate your level of risk. None of these estimates should be treated as a legal guarantee.

Understanding alcohol units

The NHS provides a useful reference for the number of units in common drinks. A pint of lower-strength lager, beer or cider (3.6% ABV) contains 2 units. A standard 175 ml glass of wine at 12% ABV contains 2.1 units. A large 250 ml glass of the same wine contains 3 units, and a small 125 ml glass contains 1.5 units. A single small shot of spirits (25 ml, 40% ABV) is 1 unit. These figures come from the NHS alcohol units guide.

The NHS formula for calculating units

If you want to calculate the number of units in any drink, the NHS formula is: ABV × volume (ml) ÷ 1,000 = units. For example, a 175 ml glass of 12% wine gives 12 × 175 ÷ 1,000 = 2.1 units. A pint of 3.6% beer gives 3.6 × 568 ÷ 1,000 = 2.0 units. This formula can help you track your total intake, but it cannot predict your blood alcohol concentration because of individual factors such as weight, sex, and metabolism.

Why a calculator cannot give a definitive answer

Drinkaware explicitly states that it is not possible to work out how many units will put someone over the legal limit, and that it varies from person to person. People can blow different readings on a breathalyzer even after drinking exactly the same amount. The only way to know your reading is with a certified breathalyzer test, and even then the legal result depends on the measured breath, blood, or urine level rather than a unit count.

Can you have a pint and drive UK?

The direct answer is that it depends on where you are, what you drink, and who you are. In Scotland, even one pint of medium-strength lager could put a woman over the limit, and a man may be over after two pints. In England, Wales and Northern Ireland, the limits are higher, but a pint is still not a guaranteed “safe” amount for everyone. The British Medical Association has warned against the dangerous misinformation that suggests up to four units can safely be drunk before driving.

The BMA stated: “Various websites suggest anything up to four units of alcohol can safely be drunk and an individual can legally drive. This is dangerous misinformation.” The organisation’s warning underscores the fact that the legal limit is not a target to aim for, and that even below the limit, impairment can occur.

The same logic applies in England, Wales and Northern Ireland. Although the limit is higher, a pint of strong lager (5% ABV) contains approximately 2.8 units, and two such pints would put a man close to or over the 4-unit rough guide. Because alcohol absorption depends on so many variables, relying on a “one pint rule” is not a reliable strategy.

When did the drink drive limits change in the UK?

The legal limits for drink driving in the UK have changed at different times in different nations. The timeline below outlines the key milestones.

1. 1967: The Road Safety Act introduces the first legal blood alcohol limit of 80mg per 100ml for England and Wales. This was a landmark moment in UK road safety.
2. 2014: Scotland lowers its drink drive limit to 50mg per 100ml of blood and 22 micrograms per 100ml of breath, adopting a stricter standard than the rest of the UK.
3. 2021: Northern Ireland adopts the same lower limit as Scotland: 50mg per 100ml of blood and 22 micrograms per 100ml of breath, replacing the previous 80mg standard.

These changes mean that as of 2025, the UK has two distinct legal limits. Drivers moving between Scotland and England, or between Northern Ireland and England, need to be aware of which limit applies. The Royal Society for the Prevention of Accidents (RoSPA) provides ongoing advice about drink driving and the risks involved.

What is certain and what remains unclear about drink drive limits?

Despite the widespread availability of guidance, there is a significant gap between what is clearly established by law and what remains uncertain for individual drivers. The table below separates the facts from the grey areas.

The uncertainty is not a loophole; it reflects the biological reality that alcohol affects people differently. This is why official sources consistently advise against trying to calculate a “safe” number of drinks and instead recommend zero alcohol before driving.

Why are units an unreliable measure for drink driving?

The legal limit for driving is measured in milligrams of alcohol per 100 millilitres of blood, or micrograms per 100 millilitres of breath. It is not expressed in “units” of alcohol. Units are a simplified public health measure (1 unit = 10 millilitres of pure alcohol) designed to help people track their total drinking over a week, not to determine fitness to drive. The drink drive limit does not have a unit equivalent in law.

Police use roadside breathalyzers to test for alcohol. A positive roadside test leads to a station test with an evidential device, which produces a legally admissible reading. That reading is compared against the legal limit in breath, blood, or urine. It is not compared against a unit count. The Drinkaware charity explains that the drink drive limits are 80 milligrams of alcohol per 100 millilitres of blood in England, Wales and Northern Ireland, and 50 milligrams in Scotland. These are the figures that matter in law.

Penalties for driving over the limit include a minimum 12-month driving ban, a fine of up to £5,000, and possible imprisonment. A conviction can also affect employment, insurance premiums, and travel to certain countries. The legal and personal consequences are significant, which is why relying on unit-based estimates is a high-risk strategy.

What do official sources say about drink driving limits?

Several authoritative organisations have published statements that clarify both the legal limits and the risks of relying on unit-based estimates. The quotes below reflect the consensus across government, medical, and charity sources.

“There are strict alcohol limits for drivers, but it’s impossible to say exactly how many drinks this equals – it’s different for each person.”

— UK Government (gov.uk)

“The drink drive limits in England, Wales and Northern Ireland are: 80 milligrams of alcohol per 100 millilitres of blood… 35 micrograms per 100 millilitres of breath.”

— Drinkaware

“Various websites suggest anything up to four units of alcohol can safely be drunk and an individual can legally drive. This is dangerous misinformation.”

— British Medical Association (BMA)

These statements reinforce the same message from different angles: the legal limit is a maximum, not a target, and no unit-based shortcut can reliably tell you whether you are safe to drive. The NHS alcohol units guide provides a helpful reference for understanding how many units are in common drinks, but it is not a driving safety tool.

What is the key takeaway for drivers?

The only reliable way to ensure you are within the legal limit is to consume zero alcohol before driving. Because the legal limit is measured in blood, breath, or urine alcohol concentration rather than in units, and because individual factors such as weight, sex, metabolism, and food intake cause significant variation, no fixed number of drinks can be considered safe for everyone. If you need information about other driving-related tasks, you can read about Check if a Vehicle is Taxed.

Frequently asked questions about drink driving units