Estimate Your Blood Alcohol Concentration (BAC)
Enter your drinking details below to estimate current alcohol concentration using a Widmark-style formula.
Important: This tool gives an estimate, not a legal or medical determination. Do not drive or operate machinery after drinking.
What this alcohol concentration calculator does
This calculator estimates blood alcohol concentration (BAC) based on body weight, alcohol amount, beverage strength, and elapsed time. BAC is commonly shown as a percent (for example, 0.08%) and indicates grams of ethanol per deciliter of blood.
We use a Widmark-style model because it is practical and widely used for educational estimates. It combines total alcohol consumed with your estimated body water distribution and subtracts a standard elimination rate over time.
How the calculation works
1) Total alcohol consumed
The calculator first converts your drinks into grams of pure ethanol:
Alcohol grams = Drinks × Volume (mL) × (ABV/100) × 0.789
Here, 0.789 g/mL is the density of ethanol.
2) Estimated concentration
Next, BAC is estimated with body weight and body water factor (r):
BAC% = (Alcohol grams / (Weight kg × 1000 × r)) × 100 − (0.015 × Hours)
The calculator floors negative values at zero. It also shows BAC in mg/dL and ‰ (permille) for reference.
How to use results responsibly
- Use this as a planning tool, not proof of sobriety.
- Legal limits vary by country and state; many places use 0.08%, while some are lower.
- Impairment can begin well below legal limits, especially for reaction time and judgment.
- If you are unsure, do not drive. Choose a ride share, taxi, public transit, or a designated driver.
Why real BAC may differ from the estimate
Actual alcohol concentration can vary significantly between people and situations. The model cannot fully capture:
- Food in the stomach and meal timing
- Drinking speed and drink size accuracy
- Medications, health conditions, hydration, and fatigue
- Individual metabolic differences
- Recent drinking still being absorbed
Quick interpretation guide
- 0.00–0.02%: minimal effects for most people
- 0.03–0.07%: mild to moderate impairment
- 0.08–0.14%: clear impairment, unsafe for driving
- 0.15–0.29%: severe impairment, high risk
- 0.30%+: potentially life-threatening intoxication
Frequently asked questions
Can I speed up alcohol elimination?
Not meaningfully. Coffee, cold showers, and exercise do not quickly reduce BAC. Time is the main factor.
Is one “drink” always equal?
No. Serving sizes and ABV vary a lot. A large craft beer can equal multiple standard drinks. Enter your actual volume and ABV when possible.
Should I rely on this for legal decisions?
No. This is an educational estimate only. If safety is involved, choose the conservative option and avoid driving after drinking.