Blood Alcohol Content Calculator
Work out whether you’re within the legal driving limits
Add Your Drinks
No drinks added yet. Click a drink type above to start.
What Does This Mean?
How to Use This Calculator
Getting an accurate estimate of your blood alcohol content is straightforward. Start by selecting your region, as legal limits vary across the UK. Then input your gender and weight, which significantly affect how your body processes alcohol.
Next, add each drink you’ve consumed by clicking the relevant drink type. You can specify the exact volume and alcohol percentage, or use our preset values for common drinks. Finally, enter how long it’s been since your first drink, as your body eliminates alcohol over time at a steady rate.
Once you’ve entered all your details, hit the calculate button to see your estimated BAC, whether you’re over the legal limit, and approximately how long until you’ll be back to zero.
Regional Limits Across the UK
| Region | Blood (mg/100ml) | Breath (µg/100ml) | Urine (mg/100ml) |
|---|---|---|---|
| England & Wales | 80 | 35 | 107 |
| Scotland | 50 | 22 | 67 |
| Northern Ireland | 80 | 35 | 107 |
Scotland introduced lower limits in December 2014, making it stricter than the rest of the UK. The Scottish limit aligns with many European countries, whilst England, Wales, and Northern Ireland maintain higher thresholds.
How BAC Calculation Works
Your blood alcohol concentration represents the percentage of alcohol in your bloodstream. This calculator uses the Widmark formula, the gold standard for BAC estimation, which accounts for the alcohol you’ve consumed, your body weight, gender, and time elapsed.
When you drink alcohol, it’s absorbed into your bloodstream through your stomach and small intestine. Your gender matters because men and women have different body water percentages – women typically have less body water, leading to higher BAC levels from the same amount of alcohol.
Your body eliminates alcohol at approximately 0.015% BAC per hour (roughly one unit per hour), though this varies between individuals. Factors like age, metabolism, medications, and liver health all play a role in how quickly you process alcohol.
What Affects Your Blood Alcohol Level?
Body Composition
Your weight and body composition significantly impact BAC. Heavier people have more blood and body water, diluting alcohol more effectively. Muscle tissue contains more water than fat, so someone with more muscle mass will typically have a lower BAC than someone of the same weight with higher body fat.
Drinking Speed
How quickly you consume alcohol matters enormously. Drinking several drinks rapidly causes BAC to spike sharply, whilst spacing drinks over hours allows your body to metabolise alcohol between drinks, keeping BAC lower.
Food Intake
Eating before or whilst drinking slows alcohol absorption. Food, especially protein and fat, keeps alcohol in your stomach longer, where absorption is slower than in the small intestine. An empty stomach leads to faster, higher BAC peaks.
Age & Health
Younger adults typically metabolise alcohol faster than older adults. Liver function, certain medications, and overall health status can significantly affect how your body processes alcohol. Those with liver conditions metabolise alcohol much more slowly.
Common Drink Measurements
| Drink Type | Typical Serving | ABV Range | Approx. Units |
|---|---|---|---|
| Pint of Beer/Lager | 568ml | 3.6% – 5.5% | 2.0 – 3.1 |
| Glass of Wine (Standard) | 175ml | 11% – 14% | 1.9 – 2.5 |
| Glass of Wine (Large) | 250ml | 11% – 14% | 2.8 – 3.5 |
| Single Spirit & Mixer | 25ml | 37% – 40% | 0.9 – 1.0 |
| Double Spirit & Mixer | 50ml | 37% – 40% | 1.9 – 2.0 |
| Bottle of Alcopop | 275ml | 4% – 5.5% | 1.1 – 1.5 |
| Pint of Cider | 568ml | 4% – 7.5% | 2.3 – 4.3 |
Frequently Asked Questions
Common Mistakes to Avoid
Misjudging Drink Strength
Many people underestimate how strong their drinks are. Wine has increased in strength over the years – many wines now contain 13-14% ABV rather than the 11-12% of decades past. Craft beers and premium lagers often exceed 5% ABV, whilst some reach 7-9%. Always check the label and input the actual ABV for accurate results.
Forgetting About Large Measures
Pub measures have grown larger. A ‘standard’ wine glass is now often 175ml or 250ml, not the 125ml small glass. Home pours are typically even more generous. When calculating, be honest about actual volumes consumed – measuring at home can be eye-opening.
Assuming You Feel Fine Means You’re Safe
You can be over the legal limit whilst feeling completely normal. Alcohol impairs judgement, including your ability to assess your own impairment. Many drivers arrested for drink-driving insist they felt fine to drive. Never rely on how you feel.
Not Accounting for the Morning After
If you finish drinking at midnight after a heavy session, you could still be over the limit at 8am or later. Your body doesn’t eliminate alcohol faster whilst you sleep. Calculate from your first drink, not your last, and add several hours to be safe.
The Science Behind Alcohol Metabolism
When alcohol enters your body, approximately 20% is absorbed through your stomach, whilst the remaining 80% is absorbed through your small intestine. This is why drinking on an empty stomach leads to faster intoxication – alcohol reaches your small intestine more quickly.
Once absorbed, alcohol is distributed throughout your body’s water content. Your liver then begins breaking it down using enzymes, primarily alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). This process converts alcohol first to acetaldehyde (toxic and responsible for hangover symptoms), then to acetic acid, which is eventually broken down into water and carbon dioxide.
Your liver can only process a certain amount of alcohol per hour – typically about 7-10 grams, equivalent to one unit. This rate is relatively constant and cannot be significantly increased. A small amount of alcohol (about 5-10%) is eliminated through breath, sweat, and urine, which is why breathalysers work.
Penalties and Legal Consequences
| Offence | Maximum Prison Sentence | Driving Ban | Maximum Fine |
|---|---|---|---|
| Driving/attempting to drive over the limit | 6 months | Minimum 12 months | Unlimited |
| Being in charge of a vehicle over the limit | 3 months | Possible ban | £2,500 |
| Causing death by careless driving whilst over the limit | 14 years | Minimum 2 years | Unlimited |
| Refusing to provide a specimen | 6 months | Minimum 12 months | Unlimited |
Beyond legal penalties, a drink-drive conviction results in a criminal record that can affect employment, travel visas (particularly to countries like the USA and Canada), and insurance premiums for years. Your driving licence will show the conviction for 11 years.