What this blood alcohol concentration calculator does
This tool estimates your blood alcohol concentration (BAC) using a classic Widmark-style formula. BAC is the amount of alcohol in your bloodstream, expressed as a percentage (for example, 0.08%). The estimate is useful for education and planning, but it is not a medical test and should never be used to decide whether it is safe to drive.
Real-world alcohol effects vary substantially by person and situation. Your hydration, food intake, medications, metabolism, fatigue, and drinking speed can all change the result. If there is any doubt, choose the safe option: do not drive.
How the estimate is calculated
Widmark-based approach
The calculator first estimates how much pure ethanol you consumed. Then it applies body weight and a distribution ratio (often called the Widmark “r” value), and subtracts a rough hourly metabolism rate.
- Total ethanol (oz) = drinks × drink size × ABV
- BAC estimate = (ethanol oz × 5.14) ÷ (weight in lb × r) − (0.015 × hours)
- The result is clamped at 0.000 minimum.
Commonly used r values in simple calculators are 0.73 for men and 0.66 for women; this page also offers a neutral middle value for unspecified selection.
How to use the calculator
Step-by-step
- Enter your body weight and choose pounds or kilograms.
- Choose a biological sex option (used for distribution ratio only).
- Input number of drinks, average drink size, and average ABV percentage.
- Enter hours since your first drink.
- Click Calculate BAC to view your estimate and interpretation.
Interpreting BAC ranges (general guide)
Effects can vary, but many references use ranges similar to these:
- 0.01–0.029: subtle mood changes possible.
- 0.03–0.059: lowered inhibition, reduced judgment.
- 0.06–0.079: impaired balance/reaction, reduced focus.
- 0.08–0.149: significant impairment; in many places 0.08 is a legal driving limit.
- 0.15–0.299: major motor/cognitive impairment, high risk of injury.
- 0.30+: potentially life-threatening alcohol poisoning risk.
What can make your BAC higher than expected?
Common reasons estimates are off
- Strong pours, oversized drinks, or unknown ABV.
- Rapid consumption over a short period.
- Low body mass or limited food intake.
- Interactions with medications or health conditions.
- Poor sleep and dehydration increasing perceived impairment.
Remember: two people with the same BAC can show very different outward behavior and impairment levels.
Safety and legal reminder
This calculator is for informational purposes only. Legal limits vary by country, state, and license type. Commercial drivers, underage drivers, and probationary drivers may face stricter limits, including zero-tolerance policies. Even below legal limits, reaction time and decision-making can still be impaired.
If you have been drinking, the safest plan is simple: use a rideshare, taxi, public transit, or a sober driver.
Frequently asked questions
Can coffee, cold showers, or exercise lower BAC quickly?
No. They may make you feel more alert, but they do not significantly accelerate alcohol elimination from blood. Time is the primary factor.
How long until BAC reaches zero?
A rough planning estimate uses a metabolism rate around 0.015 BAC per hour. This varies person-to-person. The calculator provides an approximate “time to near zero,” but treat it as a rough guideline, not a guarantee.
Is this acceptable for legal or medical use?
No. Only calibrated breath or blood testing administered under proper procedures can be used for legal or clinical determinations.