Estimate your blood alcohol content from drinks, weight, gender and time. Educational use only — never drive after drinking.
Blood alcohol content (BAC) is the concentration of alcohol in your bloodstream, expressed as a percentage. A BAC of 0.08% means 0.08 grams of alcohol per 100 millilitres of blood. BAC determines the degree of alcohol impairment — affecting judgement, coordination, reaction time and vision at progressively higher levels. Our BAC calculator uses the Widmark formula, the most widely validated method for estimating BAC, to give you an educational estimate based on your weight, gender, drinks consumed and time elapsed. BAC estimates are approximate — individual variation is significant and depends on many factors beyond these inputs. This calculator is for educational awareness only.
The Widmark formula is the standard mathematical model used to estimate BAC: BAC = (Alcohol in grams / (Body weight in grams x r)) - (0.015 x Hours). The r factor is the Widmark distribution factor, representing the proportion of the body through which alcohol distributes. For men, r = 0.68, reflecting a higher percentage of body water. For women, r = 0.55, reflecting a lower body water percentage and higher body fat percentage — both of which concentrate alcohol more effectively. One US standard drink contains 14 grams of pure alcohol. A 160lb (73kg) man drinking 3 standard drinks over 2 hours has a BAC of approximately (42 / (73,000 x 0.68)) - (0.015 x 2) = 0.085% - 0.030% = 0.055%. Use our water intake calculator to understand daily hydration needs, and our calorie calculator to see how alcohol calories fit into your daily intake.
| BAC Level | Effects | Driving Risk | Legal Status (US) |
|---|---|---|---|
| 0.01 - 0.03% | Mild relaxation, slight mood elevation | Minimal | Legal (adults) |
| 0.04 - 0.06% | Lowered inhibitions, reduced fine motor control | Slight impairment | Legal (adults) |
| 0.07 - 0.09% | Impaired judgement, reduced coordination | Significantly impaired | Illegal at 0.08%+ |
| 0.10 - 0.15% | Slurred speech, poor balance, delayed reactions | Severely impaired | Illegal |
| 0.16 - 0.20% | Nausea possible, significant disorientation | Extremely dangerous | Illegal |
| 0.25%+ | Loss of consciousness risk, medical emergency range | Cannot drive | Illegal |
The concept of a standard drink exists to give a consistent measure of alcohol consumption regardless of the type of beverage. In the United States, one standard drink contains 14 grams (0.6 fl oz) of pure alcohol. This corresponds to: 12 fl oz (355ml) of regular beer at 5% ABV, 8-9 fl oz (240ml) of malt liquor at 7% ABV, 5 fl oz (148ml) of wine at 12% ABV, or 1.5 fl oz (44ml) of distilled spirits at 40% ABV. Many real-world drinks are actually more than one standard drink. A 16oz pint of craft beer at 7% ABV is approximately 2.2 standard drinks. A large glass of wine (8oz) is approximately 1.6 standard drinks. A double shot cocktail is 2 standard drinks. Accurately counting standard drinks requires knowing the ABV and volume of each drink consumed, then calculating: standard drinks = (volume in ml x ABV) / 14,000. Overestimating the number of standard drinks is one of the most common sources of BAC calculation error.
| Drink | Typical Serving | ABV | Standard Drinks | Alcohol (grams) |
|---|---|---|---|---|
| Regular Beer | 12 fl oz (355ml) | 5% | 1.0 | 14g |
| Craft Beer (IPA) | 12 fl oz (355ml) | 7% | 1.4 | 19.6g |
| Pint Craft Beer | 16 fl oz (473ml) | 7% | 1.9 | 26.1g |
| Table Wine | 5 fl oz (148ml) | 12% | 1.0 | 14g |
| Large Wine | 8 fl oz (237ml) | 12% | 1.6 | 22.4g |
| Shot of Spirits | 1.5 fl oz (44ml) | 40% | 1.0 | 14g |
| Double Spirits | 3 fl oz (89ml) | 40% | 2.0 | 28g |
| Margarita | 8 fl oz (237ml) | ~15% | 2.5 | 35g |
The liver metabolises alcohol at an approximately fixed rate of 0.015% BAC per hour for most adults. This rate is largely independent of food intake, coffee consumption, exercise, water, cold showers or any other intervention. These factors may affect how you feel but they do not lower your BAC. The formula is simple: hours to sober = BAC / 0.015. A BAC of 0.08% takes 0.08 / 0.015 = 5.3 hours to reach zero. A BAC of 0.15% takes 10 hours. This means that alcohol consumed in the evening can still impair driving the following morning. A person who stops drinking at midnight with a BAC of 0.12% still has a BAC of approximately 0.04-0.05% at 7am. Use our age calculator to verify legal drinking age compliance, and our BMI calculator alongside this tool since body composition affects how alcohol is distributed.
The Widmark formula accounts for body weight and gender but several additional factors significantly affect real-world BAC that no formula can precisely capture. Food consumption: eating before or during drinking slows alcohol absorption by 25-50% and reduces peak BAC, though the total amount absorbed remains the same. Drinking speed: consuming drinks rapidly produces higher peak BAC than the same amount spread over more time, because the liver is already metabolising earlier drinks while later ones are absorbed. Medication interactions: many medications including antihistamines, sedatives, antidepressants and some antibiotics amplify alcohol's effects at any BAC level. Fatigue: alcohol impairs a tired person more severely than a rested person at the same BAC. Hydration: alcohol suppresses antidiuretic hormone (ADH), causing the kidneys to excrete more water than you drink — dehydration exacerbates impairment and contributes to hangover symptoms. Drinking carbonated mixers (tonic, soda) slightly accelerates alcohol absorption compared to still mixers. Individual enzyme levels: genetics determine the amount of alcohol dehydrogenase (ADH) produced in the stomach, creating genuine inter-individual variation in alcohol metabolism that can be as large as 50%.
Legal BAC limits for driving vary significantly between countries and regions. In the United States, the federal standard is 0.08% for drivers 21 and over. Commercial vehicle drivers have a limit of 0.04%. Under-21 drivers face zero tolerance laws ranging from 0.00% to 0.02% across different states. Canada, the UK, Australia and most of Europe have a standard limit of 0.05%, with some European countries including Czech Republic, Hungary and Slovakia enforcing a 0.00% limit. Japan enforces 0.03%. Research consistently shows that meaningful driving impairment begins below the legal limit in most jurisdictions — reaction time, lane tracking and hazard perception are measurably impaired at BAC levels as low as 0.02-0.04% in controlled studies. The 0.08% US legal limit represents a political and enforcement compromise rather than the threshold of impairment.
Alcohol contains 7 calories per gram — more than carbohydrates (4 cal/g) or protein (4 cal/g), but less than fat (9 cal/g). A standard drink containing 14 grams of alcohol therefore provides a minimum of 98 calories from the alcohol alone, before accounting for mixers, syrups, juice and other ingredients. A regular beer (14g alcohol + carbohydrates) is approximately 150 calories. A glass of wine is approximately 120-130 calories. A margarita can be 250-400 calories depending on the mix. Three standard drinks add 300-450 alcohol calories to your daily intake before food. Alcohol calories are often overlooked in dietary tracking because they are consumed as a liquid and are not listed prominently on menus. Use our calorie calculator to factor drink calories into your daily totals and our body fat calculator to understand how consistent alcohol consumption affects body composition over time.
Understanding your own alcohol tolerance and its limits is one of the most important safety concepts for responsible consumption. Tolerance develops through repeated exposure as the liver produces more alcohol dehydrogenase and the brain adapts to alcohol's effects — meaning a person with high tolerance may feel less impaired at a given BAC than a first-time drinker. Critically, tolerance affects how impaired you feel but not how impaired you actually are. A person with high alcohol tolerance who feels fine at 0.10% BAC is just as impaired in measurable cognitive and motor tests as a low-tolerance person at the same BAC level who feels severely intoxicated. This is why tolerance is genuinely dangerous — it disconnects the subjective sensation of impairment from the objective neurological and physiological impairment. Use our water intake calculator to understand your daily hydration baseline and our calorie calculator to accurately account for the calories in alcoholic drinks as part of your overall daily intake.