Drink Drive Limit Calculator
Estimate your blood alcohol concentration (BAC) and check whether you are within UK drink drive limits. Enter your drinks, body weight, and time elapsed to see your estimated BAC level, impairment status, and time until sober. Covers both England/Wales and Scotland limits.
BAC Estimator
Total servings consumed
Your body weight in kilogrammes
Affects body water ratio used in the Widmark formula
Scotland has a lower drink drive limit than England & Wales
UK Drink Drive Limits
England, Wales & Northern Ireland
Equivalent to 0.08% BAC. This has been the legal limit since 1967, set by the Road Safety Act.
Scotland
Equivalent to 0.05% BAC. Scotland lowered its limit in December 2014 to align with most European countries.
How to Use This Tool
Enter Your Drinks
Select your drink type from common UK servings and enter how many you have consumed
Add Your Details
Enter your body weight in kilogrammes, biological sex, UK region, and time since your first drink
Check Your BAC
See your estimated blood alcohol concentration, UK units consumed, and whether you are within the drink drive limit
UK Alcohol Units Guide
The UK measures alcohol in units. One unit equals 10 millilitres (8 grammes) of pure alcohol. The NHS recommends no more than 14 units per week, spread across three or more days.
| Drink | Typical Serving | Units |
|---|---|---|
| Pint of lager | 568 ml, 4% ABV | 2.3 |
| Pint of strong lager | 568 ml, 5.2% ABV | 3.0 |
| Large glass of wine | 250 ml, 13% ABV | 3.3 |
| Standard glass of wine | 175 ml, 13% ABV | 2.3 |
| Small glass of wine | 125 ml, 13% ABV | 1.6 |
| Single spirit | 25 ml, 40% ABV | 1.0 |
| Double spirit | 50 ml, 40% ABV | 2.0 |
Widmark Formula
BAC = (A / (W * r)) * 100 - (0.015 * t)The Widmark formula estimates BAC using these variables:
- A = total alcohol consumed in grammes (UK units x 8g)
- W = body weight in grammes
- r = Widmark factor (0.68 for males, 0.55 for females)
- t = time in hours since first drink
- 0.015 = average metabolic elimination rate (BAC per hour)
The Widmark factor accounts for differences in body water distribution between biological sexes. Males typically have a higher water-to-body-weight ratio, which dilutes alcohol more effectively.
The metabolic rate of 0.015% per hour is an average. Individual rates vary from about 0.010% to 0.020% per hour depending on liver function, genetics, and other factors.
Frequently Asked Questions
What is the drink drive limit in the UK?
In England, Wales, and Northern Ireland, the legal drink drive limit is 80 milligrammes of alcohol per 100 millilitres of blood (0.08% BAC). In Scotland, the limit is lower at 50 milligrammes per 100 millilitres of blood (0.05% BAC). There is no guaranteed safe level of drinking for driving.
What is a UK alcohol unit?
A UK alcohol unit equals 10 millilitres (8 grammes) of pure alcohol. A pint of regular-strength lager (4% ABV) is about 2.3 units, a standard glass of wine (175 ml, 13% ABV) is about 2.3 units, and a single measure of spirits (25 ml, 40% ABV) is 1 unit.
How accurate is this drink drive limit calculator?
This calculator uses the Widmark formula to estimate your blood alcohol concentration. However, actual BAC varies based on many factors including food intake, medication, liver health, hydration, and individual metabolism. This tool is for educational purposes only and should never be used to determine whether you are safe to drive. If in doubt, do not drive.
How long does it take for alcohol to leave your system?
On average, your body metabolises alcohol at a rate of about 0.015% BAC per hour, which is roughly one UK unit per hour. However, this varies between individuals. A heavy night of drinking could mean alcohol remains in your system well into the next day. The morning after is a common time for drink drive arrests in the UK.
What are the penalties for drink driving in the UK?
Penalties for drink driving in the UK include up to 6 months imprisonment, an unlimited fine, and a driving ban of at least 12 months (3 years if convicted twice in 10 years). Causing death by careless driving whilst under the influence carries a maximum of 14 years imprisonment. A conviction also leads to a criminal record and significantly higher car insurance premiums.