Estimate blood alcohol level: the ONLY safe limit is ZERO
WARNING: The ONLY safe limit is ZERO. Never drive after consuming alcohol. This calculator provides rough estimates only and is for educational purposes. Individual metabolism varies significantly. BAC depends on many factors not captured here including hydration, medication, liver function, and individual variation. If in doubt, do not drive.
Drink driving remains one of the most dangerous and heavily penalised offences on UK roads. Despite decades of campaigns, around 7,800 people are killed or injured in drink-drive collisions each year in Great Britain. The legal blood alcohol limits in the UK are 80 milligrams per 100 millilitres of blood in England and Wales, and 50 milligrams per 100 millilitres in Scotland (reduced in December 2014). However, the only truly safe limit is zero, as even small amounts of alcohol impair reaction times, judgement, and coordination. This calculator uses the Widmark formula to provide a rough educational estimate of blood alcohol concentration (BAC) based on the amount of alcohol consumed, body weight, sex, time elapsed, and whether food was consumed. It is critical to understand that this is NOT a tool to determine whether you are safe to drive. Individual variation in alcohol metabolism is enormous, and factors including hydration, medication, liver function, fatigue, and genetic differences mean that two people drinking the same amount can have very different BAC levels. The only responsible approach is: if you have consumed any alcohol, do not drive. The penalties for drink driving in the UK are severe and life-changing. A conviction results in a minimum 12-month driving ban, an unlimited fine, and a criminal record. In the most serious cases, you face up to 14 years imprisonment for causing death by careless driving while under the influence. Beyond legal consequences, drink driving devastates families and communities.
This calculator is for educational purposes only. It demonstrates how blood alcohol levels are estimated and how they compare to legal limits. It must NOT be used to decide whether to drive. 1. Enter the number of alcohol units you have consumed. One unit equals 10ml of pure alcohol, roughly half a pint of average-strength beer, a small glass of wine, or a single measure of spirits. Use our Alcohol Units Calculator if you are unsure how many units you have consumed. 2. Enter your body weight in kilograms. Body weight affects how alcohol is distributed in the body; heavier individuals generally have lower BAC per unit consumed because alcohol is distributed across more body mass. 3. Select your sex. Women typically have a higher BAC than men for the same amount of alcohol due to differences in body composition (lower water content means less dilution of alcohol). 4. Enter the hours elapsed since your first drink. The body eliminates alcohol at approximately 15 mg per 100ml of blood per hour, but this process does not begin significantly until about 30 minutes after consumption starts. 5. Indicate whether you had food. Eating before or while drinking slows alcohol absorption into the bloodstream, typically reducing peak BAC by around 30 percent. However, food does not reduce the total amount of alcohol absorbed; it only delays the peak. 6. Select your country to see the applicable legal limit. Scotland has a lower limit (50 mg/100ml) than England and Wales (80 mg/100ml). 7. Review the estimated BAC, hours until zero, and the status relative to the legal limit. Remember: these are rough estimates only. The safe limit is always zero.
The calculator uses the Widmark formula, the standard pharmacokinetic model for estimating blood alcohol concentration: **Raw BAC (mg/100ml)** = (Units x 8 x 100) / (Body weight in kg x r) Where r is the Widmark factor: 0.68 for males and 0.55 for females. This factor accounts for differences in body water content between sexes. Each alcohol unit contains 8 grams of pure alcohol, and the multiplication by 100 converts the result from g/L to mg/100ml. **Food adjustment:** If the person has eaten, the raw BAC is multiplied by 0.7 (a 30% reduction) to account for slower absorption. **Elimination:** The body eliminates alcohol at approximately 15 mg/100ml per hour. Elimination begins after an absorption period of roughly 30 minutes. The formula subtracts (hours elapsed - 0.5) x 15 from the adjusted BAC, with a minimum of zero. **Breath equivalent:** Calculated by dividing blood BAC by 2.3, the approximate blood-to-breath ratio. **Legal limits:** England and Wales: 80 mg/100ml blood (35 ug/100ml breath). Scotland: 50 mg/100ml blood (22 ug/100ml breath). For example, a 75 kg male consuming 4 units over 2 hours with food: raw BAC = (4 x 8 x 100) / (75 x 0.68) = 62.7 mg/100ml. After food adjustment: 62.7 x 0.7 = 43.9. After elimination (1.5 hours x 15 = 22.5): estimated BAC = 21.4 mg/100ml. This is below the legal limit but is NOT safe. Any alcohol impairs driving ability.
**WARNING:** This calculator provides rough estimates only. The ONLY safe limit is ZERO. Never drive after consuming alcohol. Individual metabolism varies enormously. Factors that this calculator cannot account for include: genetic variations in liver enzymes (ALDH2 deficiency affects up to 8% of the population), medication interactions (many common medications amplify alcohol effects), chronic health conditions, dehydration, fatigue, and age-related changes in metabolism. If you or someone you know has a problem with alcohol and driving, contact Drinkline on 0300 123 1110 or visit drinkaware.co.uk for confidential advice and support.