BAC
Calculator
Estimate your blood alcohol content and make safer, more informed decisions. For educational awareness only — never use this to determine fitness to drive.
Estimate Your BAC
Enter your details below for an estimated blood alcohol content reading. This is an educational estimate — actual BAC varies significantly between individuals.
👤 Personal DetailsBAC Calculator: Estimate Your Blood Alcohol Content
Blood Alcohol Content (BAC) is the measure of how much alcohol is present in your bloodstream, expressed as a percentage by weight. A BAC of 0.08% means 0.08 grams of alcohol for every 100 millilitres of blood — the legal driving limit in the United States, UK, Australia, and many other countries. This free BAC calculator uses the validated Widmark formula to estimate your blood alcohol content based on your sex, weight, number of drinks, drink type, and time elapsed — and provides safety-focused insights about what your estimated BAC means for your coordination, judgment, and legal status.
⚠️ Critical reminder: No online BAC calculator can accurately determine your legal or physical fitness to drive. Actual BAC varies widely between individuals due to liver function, genetics, medications, hydration, and other factors. If you have been drinking, the safest choice is always to not drive — regardless of what any calculator shows. Use public transport, a taxi, rideshare service, or a designated driver.
What Is BAC (Blood Alcohol Content)?
Blood Alcohol Content (BAC), also called Blood Alcohol Concentration or Blood Alcohol Level, is the standard measure used worldwide to quantify alcohol intoxication. It represents the grams of pure alcohol per 100 millilitres of blood (or per 210 litres of breath, in breathalyser measurements). The scale runs from 0.00% (completely sober) to levels that can be lethal at 0.40%+.
BAC is used by law enforcement to determine intoxication for driving offences, by medical professionals to assess alcohol poisoning, and by researchers and health authorities to study alcohol-related harm. Understanding your approximate BAC helps you make more informed decisions about activities — particularly those that require concentration, coordination, and quick reaction times, like driving, operating machinery, or caring for children.
How This BAC Calculator Works
This blood alcohol calculator uses the Widmark Formula — a mathematical model developed by Swedish physician Erik Widmark in 1932 and still used today as the foundation for most BAC estimation models. The formula estimates how alcohol distributes through the body based on your weight, sex, the amount of alcohol consumed, and the time elapsed for metabolism.
Understanding the Widmark Formula
Widmark Formula:
BAC% = (Alcohol consumed in grams × Food modifier) ÷ (Body weight in grams × r) × 100 − (β × T)
Where:
r = Widmark factor (0.68 for males, 0.55 for females — reflects body water distribution)
β = Metabolism rate (typically 0.015 g/dL per hour — range 0.010–0.025)
T = Time since drinking began (hours)
Food modifier = 1.0 (empty stomach), 0.85 (light meal), 0.65 (heavy meal) — food slows absorption, which lowers the peak BAC reached
Alcohol in grams = Volume (mL) × ABV% × 0.789 (density of ethanol)
Example: 75kg male who drank 3 beers (355ml × 5% each) over 2 hours, with a light meal (the calculator’s default):
Alcohol = 3 × 355 × 0.05 × 0.789 = 42.0g
Adjusted for food = 42.0 × 0.85 = 35.7g
BAC = (35.7 ÷ (75,000 × 0.68)) × 100 − (0.015 × 2) = 0.070% − 0.030% = 0.040% BAC
How the BAC Calculator Formula Works
This calculator estimates the concentration of alcohol in your bloodstream at a given point in time, using your body weight, biological sex, how much you drank, and how long ago you started drinking. The formula measures grams of pure alcohol relative to your body’s water volume, then subtracts however much your liver has already metabolised. The unit is a percentage: grams of alcohol per 100 millilitres of blood. Read the result as an estimate with meaningful uncertainty, not a precise measurement. The formula assumes a steady, average metabolism rate and doesn’t know your actual liver function, medications, or genetics, all of which can shift real BAC noticeably in either direction. This tool cannot tell you whether you are safe to drive. Only a certified breathalyser or blood test can measure actual BAC.
Identify the inputs
You enter body weight, sex, drink type and quantity, and time elapsed since you started drinking. Optional advanced settings let you adjust for food intake and metabolism speed.
Apply the formula
The calculator first works out total grams of pure alcohol consumed, then divides that by your body weight times the Widmark r factor to get a raw BAC, then subtracts the amount your liver has metabolised over the elapsed time.
Perform the calculation
Using the default example above: 42.0g of alcohol, adjusted to 35.7g for a light meal, divided by (75,000g × 0.68) gives a raw figure of 0.070%. Subtracting 0.030% already metabolised over 2 hours leaves an estimated 0.040% BAC.
Interpret the result
0.040% falls in the “mild impairment” range on this calculator’s scale. That still means measurably reduced coordination and reaction time, and driving is not recommended at any level above 0.00%.
3 Real-Life Examples
1. A woman having wine with dinner
A 62kg woman has 3 glasses of wine (150ml at 12% ABV each) over 1.5 hours with a light meal.
Estimated BAC: approximately 0.084%, above the 0.08% legal limit used in the US and several other countries, and well into the “significant impairment” range on this calculator’s scale. The lower female Widmark factor means the same number of standard drinks produces a noticeably higher BAC than it would for a man of similar weight.
2. A man with cocktails and a heavy meal, several hours later
An 85kg man has 2 cocktails (200ml at 14% ABV each, a strong mixed drink) with a heavy meal, then checks his estimate 3 hours after he started drinking.
Estimated BAC: approximately 0.005%, close to zero. This illustrates how a substantial meal plus enough elapsed time can bring an estimate down considerably, though it’s never a reason to assume driving is safe immediately after drinking.
3. A man who drank heavily and waited before driving
A 78kg man has 5 beers (355ml at 5% ABV each) on an empty stomach, then waits 4 hours before considering driving.
Even after waiting 4 hours, the estimated BAC is still approximately 0.072%, still in the “significant impairment” band. This is exactly the kind of situation where someone might feel like enough time has passed, when in reality heavier drinking sessions can take considerably longer than a few hours to clear completely.
The Widmark formula provides a useful approximation, but it has limitations. Individual metabolism rates vary significantly — most people metabolise alcohol at 0.012–0.020 g/dL per hour, with the average being approximately 0.015. Factors like food consumption, liver health, medications, and genetics all affect this rate in ways that no formula can capture.
What Affects Your BAC?
BAC is not determined simply by how many drinks you’ve had. Multiple physiological and behavioural factors influence how quickly alcohol is absorbed, how it distributes through the body, and how fast it is metabolised:
- Body weight: Heavier individuals have more blood and body water for alcohol to distribute into, resulting in lower BAC per drink. A 55kg person will have roughly twice the BAC of a 110kg person drinking the same amount.
- Sex: Females typically have a lower proportion of body water than males of similar weight, meaning alcohol concentrates more highly in their bloodstream. The Widmark r factor is 0.68 for males and approximately 0.55 for females, reflecting this difference.
- Food intake: Eating before or during drinking dramatically slows alcohol absorption. A fatty or protein-rich meal can reduce peak BAC by 30–50% compared to drinking on an empty stomach. Food doesn’t reduce how much alcohol you ultimately absorb — it just slows the rate of absorption, giving your liver more time to metabolise it before it reaches the bloodstream.
- Drink strength and volume: A standard drink in the US contains 14g of pure alcohol. But a pint of 8% craft beer contains significantly more alcohol than a 5% 12oz bottle — and cocktails vary enormously. Tracking standard drink equivalents rather than “number of drinks” is far more accurate.
- Time: Your liver eliminates approximately 0.015% BAC per hour (average) — regardless of coffee, water, food, or any other intervention after drinking. Only time reduces BAC.
- Medications: Many medications interact with alcohol, affecting both metabolism rate and the subjective experience of intoxication. Some medications (particularly sedatives, antihistamines, and certain antibiotics) can dramatically amplify alcohol’s effects at any given BAC level.
- Genetics: Genetic variation in alcohol dehydrogenase (ADH) enzymes means some people metabolise alcohol much faster or slower than the population average. East Asian populations have a higher prevalence of a variant that causes rapid acetaldehyde buildup, producing the “alcohol flush reaction.”
BAC Levels and Their Effects
| BAC Level | Category | Typical Effects |
|---|---|---|
| 0.00–0.03% | Sober to minimal | Little to no impairment. Mild relaxation possible. |
| 0.03–0.05% | Mild impairment | Light-headedness, slight relaxation. Minor impairment of judgement and inhibitions. |
| 0.05–0.08% | Moderate impairment | Noticeably impaired reaction time and coordination. Reduced inhibitions. Many countries’ DUI threshold. |
| 0.08–0.15% | Significant impairment | Clear speech and balance problems. Reaction time severely reduced. Memory impairment begins. US/UK/AU DUI limit. |
| 0.15–0.20% | Severe impairment | Disorientation, nausea, double vision. Significant loss of motor control. High accident risk. |
| 0.20–0.30% | Very high risk | Potential blackout, loss of consciousness. Vomiting while unconscious (aspiration risk). Medical emergency territory. |
| 0.30%+ | Medical emergency | Life-threatening. Respiratory depression, potential coma or death. Requires immediate medical attention. |
Legal BAC Limits Explained
Legal driving BAC limits vary around the world, with most developed nations setting limits between 0.05% and 0.08%. Several countries have adopted 0.00% (zero tolerance) for new or young drivers, and some countries maintain zero tolerance for all drivers.
| Country / Region | General limit | New driver limit |
|---|---|---|
| United States | 0.08% | 0.02% (most states) |
| United Kingdom | 0.08% (England/Wales); 0.05% (Scotland) | Same |
| Australia | 0.05% | 0.00% |
| Canada | 0.08% (criminal); 0.05% (licence suspension) | 0.00% |
| European Union (most) | 0.05% | 0.02% |
| Germany | 0.05% | 0.00% |
| Japan | 0.03% | 0.00% |
| Singapore | 0.08% | 0.00% |
| Sweden / Norway / Poland | 0.02% | 0.00% |
| Brazil / Russia / UAE | 0.00% | 0.00% |
It’s critical to understand that the legal limit does not define a “safe” level of driving. Research consistently shows measurable impairment in reaction time, lane-keeping, and hazard perception beginning at approximately 0.02–0.03% BAC, well below the legal threshold in most countries. NHTSA’s data on drunk driving shows crash risk rises sharply as BAC increases, even among drivers below common legal limits. The legal limit is a pragmatic enforcement boundary, not a safety guarantee.
How Long Alcohol Stays in Your System
The body metabolises alcohol at a relatively constant rate — approximately 0.015% BAC per hour for the average person, regardless of attempts to accelerate the process. Common myths about “sobering up” — including drinking coffee, cold showers, energy drinks, exercise, or eating after drinking — do not accelerate alcohol metabolism. They may make you feel more alert, but they do not reduce your actual BAC.
Time to sober guide (approximate):
Starting BAC 0.08%: fully sober in approximately 5.3 hours
Starting BAC 0.10%: fully sober in approximately 6.7 hours
Starting BAC 0.15%: fully sober in approximately 10 hours
Starting BAC 0.20%: fully sober in approximately 13+ hours
Note: “sober” here means reaching 0.00% BAC. Some cognitive and coordination impairment from alcohol can persist beyond the point of 0.00% BAC, particularly after heavy drinking sessions.
Drinking Responsibly
Eat before and during drinking
Food — particularly meals with protein, fat, and carbohydrates — slows alcohol absorption and significantly reduces peak BAC. Never drink on a completely empty stomach.
Alternate with water
Alcohol is a diuretic — it causes dehydration, which worsens hangover symptoms. Drinking a glass of water between each alcoholic drink slows consumption and reduces dehydration effects.
Pace your drinks
Drinking no more than one standard drink per hour keeps BAC low enough for your liver to approximately keep pace with metabolism. This is the most effective rate-control strategy.
Plan your transport before you start
Arrange a designated driver, book a taxi, or plan your rideshare route before the first drink — not after. Decision-making impairment begins well before the legal driving limit.
Use a breathalyser, not an app
No BAC calculator, including this one, is a substitute for an actual certified breathalyser. If you need to know your actual BAC before driving, only a calibrated breathalyser or blood test provides reliable data.
Look out for those around you
If someone appears heavily intoxicated — slurred speech, inability to stand, confusion — do not leave them alone. Place them in the recovery position if they are unconscious. Call emergency services if concerned about their breathing.
Common Myths About Alcohol
- Myth: Coffee sobers you up. Caffeine makes you feel more alert but does not reduce BAC. It produces a “wide-awake drunk” — someone who feels more capable but is still significantly impaired.
- Myth: A cold shower will sober you up. Cold water stimulates the nervous system temporarily but has no effect on alcohol metabolism or BAC levels.
- Myth: Beer is safer than spirits. A pint of 5% beer and a double shot of 40% spirits both contain approximately the same amount of alcohol (about 14g). Drink type doesn’t determine BAC — pure alcohol content does.
- Myth: I feel fine, so I’m under the limit. Tolerance is not the same as safety. Experienced drinkers often show fewer subjective signs of impairment at high BAC levels, but objective measures — reaction time, lane tracking, hazard perception — remain impaired regardless of how you feel.
- Myth: Eating after drinking helps. Food before drinking slows absorption significantly. Food after drinking has minimal effect since the alcohol is already in the bloodstream.
- Myth: Switching between drink types makes you more drunk. BAC is determined by total alcohol consumed, not by mixing types. “Beer before wine, feeling fine” has no scientific basis.
When to Seek Help
If you or someone you know is experiencing signs of alcohol poisoning — confusion, unconsciousness, seizures, slow or irregular breathing, blue-tinged or pale skin, vomiting while unconscious — call emergency services immediately. Alcohol poisoning is a medical emergency.
If alcohol consumption has become difficult to control or is causing problems in relationships, work, or health, please reach out to a healthcare professional, addiction counsellor, or alcohol support service. SAMHSA’s National Helpline (1-800-662-4357) is a free, confidential, 24/7 service in the US offering treatment referrals. Resources available in many other countries include Alcoholics Anonymous (AA) and SMART Recovery.
Important Notes
What this calculator does and doesn’t cover
This tool applies the Widmark formula to the numbers you enter. A few things worth understanding before relying on it:
- This is an estimate, not a measurement. Only a certified breathalyser or a blood test measures your actual BAC. This calculator cannot know your liver function, medications, hydration, or genetics, all of which affect real BAC.
- Never use this to decide whether to drive. Impairment in reaction time and judgment begins well below the legal limit in most places. According to NHTSA’s data on drunk driving, crash risk rises sharply even at BAC levels below common legal thresholds.
- Standard drink sizes are approximations. The drink presets follow the NIAAA’s definition of a standard drink (about 14g of pure alcohol), but real pours, cocktails, and craft beers vary widely from these standard sizes.
- Only time reduces BAC. No amount of coffee, food, cold water, or exercise speeds up alcohol metabolism after drinking has already occurred.
- Legal limits vary by country and are not a safety guarantee. Check your local jurisdiction’s limit, and remember that “legal” does not mean “safe to drive.”
- If alcohol use feels difficult to control, support is available. SAMHSA’s National Helpline (1-800-662-4357) offers free, confidential, 24/7 support and treatment referrals.
Related Health Tools
Frequently Asked Questions
Use This Tool for Awareness, Not Permission
This BAC estimator is an educational tool to help you understand how alcohol affects your body. Never use it to decide whether to drive. When in doubt — don’t.
Estimate my BAC ↑