BAC Calculator UK
Estimate your Blood Alcohol Concentration with UK drinks, metric measurements, and drink driving limits for England, Wales, Northern Ireland, and Scotland. Uses the Widmark formula for forensic-grade estimation.
Looking for the US version? Try our US BAC Calculator.
BAC Estimator
2.8 UK units per serving
How many servings of the selected drink
Weight in kilogrammes
Determines the body water ratio used in the Widmark formula
How to Use This BAC Calculator
Choose Your Drink
Select from 20 pre-configured UK drinks with exact ABV and volume in millilitres, or toggle custom mode to enter your own drink specs
Enter Your Details
Add your body weight (kg or stone), biological sex, number of servings, and hours since your first drink
Review Your BAC Curve
See your current and peak BAC, time until sober, time until below UK legal limits, and a projected timeline with UK alcohol units
UK Drink Driving Limits
England, Wales & Northern Ireland
The drink driving limit is 80 milligrammes of alcohol per 100 millilitres of blood (0.08% BAC), 35 microgrammes per 100 millilitres of breath, or 107 milligrammes per 100 millilitres of urine.
England, Wales, Northern Ireland
Scotland
Scotland reduced its drink driving limit in December 2014 to 50 milligrammes of alcohol per 100 millilitres of blood (0.05% BAC), 22 microgrammes per 100 millilitres of breath, or 67 milligrammes per 100 millilitres of urine.
Scotland
New & Young Drivers
Whilst there is no formal zero-tolerance law in the UK, the advice from all UK police forces is clear: the safest limit is none. Any amount of alcohol impairs your ability to drive safely.
All UK jurisdictions (advisory)
Commercial & Professional Drivers
Professional drivers (HGV, PSV, taxi) are subject to the same legal limits, but employers and licensing authorities may enforce stricter policies. Many operators require zero alcohol.
All UK jurisdictions
UK Alcohol Units Guide
In the UK, alcohol is measured in units. One unit equals 10ml (8g) of pure alcohol. The NHS recommends no more than 14 units per week, spread over three or more days with several drink-free days.
Widmark Formula Details
BAC = (A / (W x r)) x 100 - (0.015 x t)This calculator converts your drink into grammes of pure alcohol using the formula:
A (grammes) = volume (ml) x ABV x 0.789 (g/ml density)Then the Widmark formula variables are:
- A = total grammes of pure alcohol consumed
- W = body weight in grammes (kg x 1000)
- r = Widmark factor: 0.68 for males, 0.55 for females
- t = hours since first drink
- 0.015 = average metabolic elimination rate (BAC% per hour)
The Widmark factor reflects the difference in total body water between biological sexes. Males average about 68% body water by weight, females about 55%. Since alcohol distributes through body water, a lower water ratio produces a higher BAC for the same amount of alcohol.
The metabolic elimination rate of 0.015% per hour is a population average. Individual rates range from about 0.010% to 0.020% per hour depending on genetics, liver health, and chronic alcohol exposure.
Frequently Asked Questions
What is the drink driving limit in the UK?
In England, Wales, and Northern Ireland, the limit is 80 milligrammes of alcohol per 100 millilitres of blood (0.08% BAC). Scotland has a lower limit of 50 milligrammes per 100 millilitres of blood (0.05% BAC), which was introduced in December 2014. However, all UK police forces advise that the safest amount of alcohol before driving is none.
What is a UK alcohol unit?
One UK alcohol unit equals 10 millilitres (8 grammes) of pure alcohol. A single 25ml measure of spirits (40% ABV) is 1 unit. A standard 175ml glass of wine (12% ABV) is 2.1 units. A pint of regular-strength lager (4% ABV) is 2.3 units. The NHS recommends no more than 14 units per week, spread over three or more days.
How accurate is a BAC calculator?
BAC calculators provide estimates, not exact measurements. Actual BAC depends on factors the formula cannot capture: food in your stomach, hydration, liver health, medications, genetics, and the rate at which you consumed drinks. The only way to know your true BAC is with a calibrated breathalyser or blood test. Never rely on a calculator to decide whether you are safe to drive.
What is the Widmark formula?
The Widmark formula (BAC = A / (W x r) x 100 - beta x t) was developed by Erik Widmark in 1932 and remains the standard for forensic BAC estimation. It uses total grammes of alcohol consumed (A), body weight in grammes (W), a gender-based body water constant (r: 0.68 male, 0.55 female), and an average metabolic elimination rate (beta: 0.015% per hour) to estimate blood alcohol concentration.
How long does it take to sober up?
Your body eliminates alcohol at roughly 0.015% BAC per hour, regardless of your weight or sex. This means one UK unit (10ml pure alcohol) typically takes about one hour to metabolise. Nothing speeds this up significantly - coffee, cold showers, and food do not accelerate alcohol metabolism. The only remedy is time. This is why many drink driving offences occur the morning after heavy drinking.
What are the penalties for drink driving in the UK?
Drink driving in the UK can result in a minimum 12-month driving ban, an unlimited fine, up to 6 months in prison, and a criminal record. Causing death by careless driving whilst under the influence carries a maximum sentence of 14 years imprisonment. A drink driving conviction stays on your licence for 11 years and will significantly increase your car insurance premiums.
Looking for the US Version?
Our US BAC Calculator uses US standard drinks, imperial measurements, and state-by-state legal limits. This UK version uses metric measurements, UK alcohol units, and provides drink driving limits for England, Wales, Northern Ireland, and Scotland.