Estimate Blood Alcohol Concentration (BAC)
Enter your details below to get an educational estimate of your blood alcohol concentration.
This tool is for informational use only. Results are approximate and not legal or medical advice. Many factors can change actual BAC, including food intake, medications, metabolism, and drink size. Never drive after drinking.
How this alcohol blood calculator works
This calculator estimates your blood alcohol concentration (BAC), which is the amount of alcohol in your bloodstream. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. In many places, 0.08% is a legal driving limit for adults, but limits vary by country and situation.
The estimate uses the well-known Widmark approach: alcohol consumed, body weight, distribution factor, and time elapsed. Because it is a model, it can never perfectly match your true BAC from a breath or blood test.
BAC = (A × 5.14 / (W × r)) − (β × H)
- A = total alcohol in fluid ounces (standard drinks × 0.6)
- W = body weight in pounds
- r = alcohol distribution ratio (0.73 male, 0.66 female)
- β = elimination rate per hour (default 0.015)
- H = hours since first drink
What counts as one standard drink?
A standard drink in the U.S. contains about 14 grams of pure alcohol, which is roughly 0.6 fluid ounces of ethanol. That is approximately:
- 12 oz regular beer at 5% ABV
- 5 oz wine at 12% ABV
- 1.5 oz distilled spirits at 40% ABV
If your servings are larger or stronger than these examples, your true BAC may be higher than you expect.
How to interpret your result
Common BAC ranges and expected effects
- 0.01–0.03: Mild relaxation, subtle effects.
- 0.04–0.06: Reduced judgment and divided attention.
- 0.07–0.09: Noticeable impairment in reaction time and coordination.
- 0.10–0.14: Significant motor and cognitive impairment.
- 0.15+: Major impairment and increased risk of alcohol poisoning.
Even at low levels, impairment can begin earlier than people realize. Sleep deprivation, stress, illness, and mixed substances can make impairment worse.
Important limitations of BAC calculators
BAC calculators are useful for awareness, not certainty. Two people with the same drink count may have very different blood alcohol levels. Key variables include:
- How quickly drinks were consumed
- Food in the stomach and hydration status
- Body composition and genetics
- Medications and health conditions
- Actual ABV and pour size (often underestimated)
For this reason, you should never use a BAC estimate to decide whether it is safe to drive.
Safer planning strategies
Before drinking
- Set a drink limit and pace before social events.
- Arrange a sober ride home in advance.
- Eat a full meal and drink water.
During drinking
- Alternate alcohol with non-alcoholic drinks.
- Avoid mixing alcohol with sedatives or other substances.
- Track each drink honestly (size and ABV matter).
After drinking
- Allow enough time for alcohol elimination.
- Sleep and recover before safety-critical tasks.
- If in doubt, do not drive.
FAQ
Can coffee or a cold shower lower BAC?
No. They may increase alertness temporarily, but only time lowers BAC.
How fast does BAC go down?
A common estimate is around 0.015 BAC per hour, though personal rates vary.
Is this calculator valid worldwide?
The physiology model is broadly applicable, but legal limits differ by region. Always follow local law.
Final note
This alcohol blood calculator is best used as a caution tool. If your estimate is near any legal threshold, assume you are impaired and choose the safer option. Better yet, plan transportation before the first drink.