Estimate Blood Alcohol Concentration (BAC)
Use this educational tool to estimate alcohol concentration in your bloodstream at a point in time.
What this alcohol in bloodstream calculator does
This calculator estimates your Blood Alcohol Concentration (BAC), which is the amount of alcohol in your blood. The result is shown in percent BAC (for example, 0.08%), with a rough interpretation range. It uses a Widmark-style model with an elimination rate over time.
How the estimate is calculated
1) Convert drinks into grams of alcohol
The tool multiplies drink volume (mL), ABV (%), and ethanol density (0.789 g/mL) to estimate grams of alcohol per drink:
- Alcohol grams per drink = volume × (ABV/100) × 0.789
- Total alcohol grams = alcohol grams per drink × number of drinks
2) Estimate distribution in body water
Alcohol distributes primarily in body water. The Widmark constant (r) approximates this:
- Male: r ≈ 0.68
- Female: r ≈ 0.55
Initial BAC is estimated from total alcohol mass divided by body mass and distribution constant.
3) Subtract metabolized alcohol over time
Most people metabolize alcohol at roughly 0.015% BAC per hour, but real rates vary. The calculator subtracts:
- Metabolized BAC = elimination rate × hours since first drink
The final BAC is never shown below zero.
Understanding your result
- 0.00%–0.03%: Mild or minimal effects possible
- 0.03%–0.08%: Noticeable impairment likely
- 0.08%+: Significant impairment and illegal for driving in many regions
- 0.15%+: High risk, severe impairment
Legal thresholds vary by country, state, and license type. Always follow local law.
Why this is only an approximation
Real BAC can differ significantly from model estimates due to:
- Food intake and stomach emptying speed
- Drinking pattern (all at once vs spread out)
- Medication interactions
- Age, liver health, hydration, sleep, and genetics
- Measurement and serving-size errors
Practical safety guidance
- Do not drive after drinking, even if your estimated BAC seems low.
- Use rideshare, public transit, or a sober driver.
- If someone is confused, vomiting repeatedly, or hard to wake, seek emergency help.
- If in doubt, wait longer; alcohol clears slowly and unpredictably.
Quick example
Suppose a 75 kg person has 3 drinks, each 355 mL at 5% ABV, over 2 hours. The calculator estimates total alcohol intake, applies Widmark distribution, then subtracts metabolism. The final value may fall near or above common legal limits depending on inputs.
FAQ
Can I use this to know when I am safe to drive?
No. Use it for education only. Never rely on an estimate for driving decisions.
What elimination rate should I use?
0.015% per hour is a common average. Some people are slower or faster. If unsure, keep the default and add a generous safety margin.
Does coffee or a shower lower BAC?
No. Time is the primary factor that lowers BAC. Stimulants may change how alert you feel, but do not remove alcohol from blood faster.