Blood Alcohol Calculator
See how alcohol clears your system over time — an educational estimate, never a fitness-to-drive test.
Blood Alcohol Calculator — your inputs
- Sex
- Male
- Age
- 30 yrs
- Height
- 175 cm
- Weight
- 70 kg
- Standard drinks
- 3
- Hours since first drink
- 2 hrs
- Food
- Light meal or snack
- Unit system
- Metric
Key takeaways
- This cannot tell you whether you are safe to drive, and neither can any other calculator. If you have been drinking, do not drive.4
- Alcohol is eliminated at a roughly constant rate — about 0.015 percentage points an hour — so the only thing that lowers blood alcohol is time. Not coffee, food, a cold shower or exercise.
- Alcohol distributes into body water, not body weight, which is why two people of the same weight can reach different concentrations from the same drinks.1
- Impairment of reaction time, tracking and divided attention begins well below every legal limit.4
- A heavy night can still be measurable at breakfast. At 0.015%/hour, a peak of 0.16% takes over ten hours to clear.
How to use this calculator
Enter your sex, age, height and weight — all four feed the body-water estimate that alcohol distributes into.
Enter how many US standard drinks you have had (14 g of alcohol each — see the table below for what counts as one) and how long it has been since the first.
Read the clearance times rather than the headline number. They are the part of this that is actually useful.
Understanding your result
Alcohol is eliminated at a roughly constant rate — around 0.015 percentage points per hour — regardless of how much you have drunk. That is why the only thing that lowers blood alcohol is time, and why a heavy night can still be measurable the next morning.
The range shown spans the published variation in elimination rate between people. Real variation is wider still: the same dose in the same person can produce meaningfully different concentrations on different days.
Food does not speed up elimination. It slows absorption, which lowers and delays the peak — a real effect, but a different one.
What this page is for
Never use this to decide whether to drive
Every published equation carries wide variation between people and within the same person on different days, none of them models absorption in real time, and impairment starts below any legal threshold. This calculator exists to show you the shape of alcohol metabolism — how slow it is, and how long it lasts. It is not a breathalyser and must never be used as one.
With that said, the shape is genuinely worth understanding, because almost everything people believe about sobering up is wrong. Elimination is close to linear and close to fixed. Whatever raises the peak — drinking faster, drinking on an empty stomach, being smaller — does not change how quickly it comes back down.
How the estimate is built
Erik Widmark's equation, published in the 1930s, is still the basis of forensic alcohol calculation.2 It divides the mass of alcohol consumed by the mass of body it distributes into, then subtracts what has been eliminated since drinking began.
Widmark's original used a fixed factor per sex to represent that volume of distribution. This calculator uses Watson's total body water equations instead, which estimate it from height, weight, age and sex.1 That is the better approach because alcohol dissolves in water and not in fat, so body composition — not sex as such — is what actually governs the concentration reached.
| Step | What it does |
|---|---|
| Standard drinks × 14 g | Converts drinks to grams of ethanol3 |
| Watson total body water | Estimates the litres of water the alcohol spreads into1 |
| × 0.806 | Blood is about 80.6% water, converting body-water concentration to blood concentration |
| − 0.015 × hours | Subtracts elimination since the first drink |
The result is shown as a range rather than a single figure, spanning the published spread of elimination rates from roughly 0.012 to 0.020 percentage points per hour. Real variation is wider than that, which is the point of showing a range at all.
What counts as one standard drink
| Drink | Serving | Strength |
|---|---|---|
| Regular beer | 12 fl oz (355 mL) | 5% ABV |
| Malt liquor | 8–9 fl oz (250 mL) | 7% ABV |
| Table wine | 5 fl oz (150 mL) | 12% ABV |
| Fortified wine | 3–4 fl oz (100 mL) | 17% ABV |
| Spirits | 1.5 fl oz (44 mL) | 40% ABV |
The serving is the thing people get wrong
Craft beer at 7–9% ABV in a 16 oz can is between two and three standard drinks, not one. A cocktail made with two spirits is two. Counting glasses rather than standard drinks is the most common reason an estimate comes out far too low.
Why nothing speeds up elimination
Around 90% of the alcohol you drink is metabolised in the liver, mostly by alcohol dehydrogenase converting it to acetaldehyde. That enzyme system is saturated at very low concentrations, which means it works at essentially its maximum rate the whole time there is alcohol present. More alcohol does not make it work faster; it simply takes longer.
- Coffee does not change elimination. It can make an intoxicated person feel alert while leaving them just as impaired — arguably more dangerous than being visibly drunk.
- Food slows absorption, lowering and delaying the peak. Eaten after drinking it does almost nothing.
- Exercise and sweating clear a negligible fraction. Around 5–10% leaves through breath, sweat and urine, and that share does not increase meaningfully with activity.
- Cold showers and fresh air change alertness, not blood alcohol.
- Vomiting removes only what is still in the stomach, not what has already been absorbed.
Impairment starts before the legal limit
| BAC | Commonly observed effects |
|---|---|
| 0.02% (warning) | Some loss of judgement; decline in visual tracking and ability to divide attention |
| 0.05% (warning) | Reduced coordination, slower response to emergencies, impaired steering |
| 0.08% (danger) | Poor muscle coordination, impaired concentration, short-term memory loss, impaired speed control |
| 0.10% (danger) | Clear deterioration in reaction time and control; slurred speech |
| 0.15% (danger) | Substantial loss of balance and vehicle control; vomiting common |
Note where the table starts. Measurable impairment of divided attention — the exact skill driving demands — appears around 0.02%, which is roughly one drink for many adults. Legal limits are a policy threshold for enforcement, not a line below which driving is unaffected.
On drinking generally
The World Health Organization's position is that no level of alcohol consumption is safe for health, and that risk begins with the first drop.5 That is a statement about long-term population risk rather than about any single evening, but it is the current evidence-based framing and it belongs on this page.
Terms used on this page
- Widmark factor
- The fraction of body mass that alcohol distributes into — historically a fixed constant per sex, around 0.68 for men and 0.55 for women. This calculator estimates it from body water instead, which handles differences in body composition that a fixed constant cannot.
- Total body water
- All the water in the body, roughly 50–60% of mass in adults. Alcohol dissolves in it and not in fat, so it is the volume that determines what concentration a given dose produces.
- Zero-order elimination
- Clearance at a fixed amount per unit of time rather than a fixed percentage. Alcohol behaves this way at all but the very lowest concentrations, which is why the decline is a straight line rather than a curve.
The formula
- Man, 30 years, 180 cm, 70 kg → TBW ≈ 42.5 L
- Three standard drinks = 42 g of alcohol
- Peak = (42 × 0.806) / 425 ≈ 0.080%
- After 2 hours: 0.080 − (0.015 × 2)
Source: Widmark with Watson body water. Published clinical/scientific formula.
Limitations
- This cannot tell you whether you are safe or legal to drive, and no calculator can. If you have been drinking, do not drive.
- Impairment of reaction time, judgement and divided attention begins well below any legal threshold, and is not the same thing as blood alcohol concentration.
- The model assumes alcohol has been fully absorbed and distributed. In the first 30–90 minutes of drinking, the real figure can be well above or below this estimate.
- It does not account for tolerance, liver disease, medications, or the substantial day-to-day variation within the same person.
- Standard drink sizes vary by country. This calculator uses the US standard drink of 14 g; a UK unit is 8 g.
References
- 1.Total body water volumes for adult males and females estimated from simple anthropometric measurements. Watson et al., American Journal of Clinical Nutrition 33(1):27–39, 1980.
- 2.The estimation of blood alcohol concentration: Widmark revisited. Posey & Mozayani, Forensic Science, Medicine and Pathology 3(1):33–39, 2007.
- 3.What Is A Standard Drink?. National Institute on Alcohol Abuse and Alcoholism, 2024.
- 4.Alcohol and Public Health: Impaired Driving. Centers for Disease Control and Prevention, 2024.
- 5.No level of alcohol consumption is safe for our health. World Health Organization Regional Office for Europe, 2023.
Frequently asked questions
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Open calculatorNot medical advice. This calculator is for general informational purposes only and is not a substitute for professional medical guidance. Always consult a qualified healthcare provider before making decisions about your health. Read the full medical disclaimer.
Printed from mystatura.com — for general information only, not medical advice.