Blood Alcohol Calculator
Estimate your blood alcohol concentration (BAC) based on what you drank, your body weight, sex, and drinking time. See your driving risk and when alcohol may be mostly cleared from your system.
This calculator provides estimates only. Individual BAC varies based on many factors. Do not use this as a substitute for legal or medical advice, and never drive if you feel impaired.
Your Estimated BAC Result
Based on your inputs, here is your estimated blood alcohol concentration, driving risk, and an approximate timeline for when alcohol may be mostly cleared.
Estimated BAC right now
Impairment right now
—Driving risk right now
—Estimated time to clear
BAC metabolism timeline
Shows estimated BAC over time from the end of drinking until fully cleared.
What Your BAC Level Means
Blood alcohol concentration (BAC) is measured as a percentage of alcohol in the bloodstream. Even modest increases can meaningfully affect judgment, coordination, and reaction time.
Effects vary by individual based on tolerance, body composition, food intake, fatigue, and other factors. Higher BAC levels generally increase both impairment and risk.
Can You Drive After Drinking?
BAC provides an estimate, but it is not the only factor that determines driving safety. Here is what the evidence generally suggests.
Even moderate BAC affects driving
Reaction time, lane-keeping accuracy, and hazard perception can decline at BAC levels well below legal limits. Some impairment begins before it feels noticeable.
Legal limits vary by location
Many countries set limits between 0.05% and 0.08%. Some regions have stricter rules for commercial drivers, young drivers, or novice licence holders. A BAC below a legal limit does not guarantee safe driving.
Lower BAC does not mean safe to drive
Individual responses to alcohol vary significantly. Tiredness, medication, and low tolerance can amplify effects at any BAC level. If you are unsure, do not drive.
When in doubt, don't drive
If your estimated BAC is elevated, or if you feel any impairment at all, the safest choice is not to drive. Arrange an alternative before drinking, not after.
How Long Alcohol May Stay in Your System
Alcohol is cleared gradually — on average around 0.015% BAC per hour for most adults. The table below shows rough estimates of how long different BAC levels may take to return closer to 0.00%, assuming no additional drinking.
| Estimated BAC | Approximate time to clear | Context |
|---|---|---|
| 0.02% | ~1–2 hours | Two light beers over an hour |
| 0.04% | ~2–3 hours | Two standard drinks over an hour |
| 0.06% | ~3–4 hours | Three drinks over an evening |
| 0.08% | ~4–6 hours | Common legal driving limit in many regions |
| 0.10% | ~5–7 hours | Significant impairment expected |
| 0.15% | ~8–10+ hours | Heavy drinking session |
Clearance rate averages approximately 0.015% per hour. This varies by individual based on liver function, body weight, sex, food intake, and other factors. Sleep does not speed up alcohol metabolism.
How Different Drinks Add Up
The same number of drinks can represent very different amounts of alcohol depending on what you're drinking. Understanding this helps explain why BAC can rise faster than expected.
| Drink | Typical serving | Typical ABV | Alcohol units (approx.) |
|---|---|---|---|
| Beer | 330 ml | 5% | ~1.3 |
| Wine | 150 ml | 12% | ~1.4 |
| Spirits | 45 ml | 40% | ~1.4 |
| Strong beer | 330 ml | 8% | ~2.1 |
| Cocktail | varies | varies | varies |
Multiple drinks over a short period can raise BAC quickly, especially with stronger drinks or larger servings. Drinking with food slows absorption but does not reduce total alcohol load.
What Affects Your BAC?
Two people who drink the same amount can have significantly different BAC levels. These are the main variables that shift the result.
Body Weight
A lower body weight generally leads to a higher BAC for the same alcohol intake, as the alcohol is distributed across less body mass.
Sex
Body composition differs between sexes, affecting how alcohol is distributed. Standard BAC formulas apply different factors for male and female bodies.
Drinking Time
The shorter the drinking period, the less time your body has had to process alcohol before the next drink arrives. Pace matters significantly.
Drink Strength
Higher ABV drinks raise BAC more quickly than lower ABV options at the same volume. A 40% spirit in a 45 ml shot delivers the same alcohol as most standard beers.
When Alcohol May Still Affect You
BAC falling does not mean impairment has disappeared. There are several reasons why effects can linger beyond what the number suggests.
You may still feel impaired even while BAC is falling. The body processes alcohol at a steady rate, but subjective effects do not always track linearly with the number.
Coordination and decision-making can remain noticeably affected for some time after peak BAC. Fatigue from a long evening can amplify this.
Sleep after drinking does not speed up alcohol metabolism. If you sleep while BAC is still elevated, some alcohol will remain in your system when you wake up.
The morning after a heavy drinking session, BAC may still be measurable. Driving the morning after is a genuine risk that is often underestimated.
Blood Alcohol Calculator FAQ
Common questions about BAC estimation, alcohol metabolism, and driving safety.
This calculator uses a version of the Widmark formula, which estimates BAC from total alcohol consumed, body weight, sex-based distribution factor, and time elapsed. The formula is: BAC = (alcohol in grams / (body weight in grams × distribution factor)) × 100, minus a time-based metabolism deduction of approximately 0.015% per hour.
That depends on your estimated BAC, how you personally feel, and the legal limit in your location. Legal driving limits vary — commonly between 0.05% and 0.08% in many countries. However, even a BAC below the legal limit can affect reaction time and judgment. If you feel any impairment, do not drive.
Alcohol is metabolised at roughly 0.015% BAC per hour on average. A BAC of 0.08% would take approximately 5–6 hours to reach near zero. Higher BAC levels take proportionally longer. Sleep does not speed up this process — only time does.
Yes. For the same amount of alcohol, a person with a lower body weight will generally have a higher BAC, because the alcohol is distributed across less body mass. This is one of the key variables in standard BAC estimation formulas.
Yes. Standard BAC formulas use different body water distribution factors for male and female bodies — typically around 0.68 for males and 0.55 for females. This reflects average differences in body composition, which affect how alcohol is distributed in the body. The result is that for the same intake and weight, estimated BAC tends to be higher for female bodies.