BAC Calculator
Estimate blood alcohol content (BAC) from the number of standard drinks, your body weight, sex and the hours since you started drinking. This is a rough educational estimate. Never use it to decide whether you can drive, because the only safe amount before driving is none.
Show steps
How to use the BAC Calculator
- Enter how many standard drinks you had, your weight and your sex.
- Enter the hours since your first drink.
- Press Calculate for an estimated BAC and the time until it reaches about zero. Treat it as an estimate, not a safety test.
Formula and method
This calculator uses the Widmark formula: BAC (%) = (A × 5.14) / (W × r) − 0.015 × t, where A is pure alcohol in ounces (a standard drink is about 0.6 oz), W is body weight in pounds, r is the distribution ratio (0.73 for men and 0.66 for women on average) and t is hours since drinking began. The body eliminates roughly 0.015% BAC per hour on average, but the rate varies between people.
What counts as one standard drink in the US
| Drink | Standard serving | Alcohol |
|---|---|---|
| Regular beer (about 5%) | 12 fl oz | 0.6 oz |
| Wine (about 12%) | 5 fl oz | 0.6 oz |
| Distilled spirits (40%) | 1.5 fl oz | 0.6 oz |
| Malt liquor (about 7%) | 8 to 9 fl oz | 0.6 oz |
Craft beers, cocktails and large pours often contain two or more standard drinks.
BAC levels and effects
| BAC | Typical effects |
|---|---|
| 0.02% | Mild relaxation, slightly reduced attention |
| 0.05% | Lower inhibition, reduced coordination |
| 0.08% | Legal driving limit in most US states; impaired judgment, balance and reaction time |
| 0.15% | Major loss of control, vomiting likely |
| 0.30% and above | Risk of loss of consciousness and death |
Utah sets its limit at 0.05%, and commercial drivers and drivers under 21 face stricter limits.
Why the estimate can be wrong
Body composition, food in the stomach, medications, how fast you drank, hydration and genetics all change BAC. Two people of the same weight can differ by 0.02% or more. If you have been drinking, arrange a ride. The NIAAA provides guidance on alcohol and the body. If you or someone you know needs help with drinking, contact the SAMHSA National Helpline at 1-800-662-4357.
Frequently asked questions
How many drinks to reach 0.08 BAC?
For a 180 lb man it takes about 4 drinks in one hour or fewer; for a 140 lb woman, about 3. This estimate varies widely.
How long does it take to sober up?
About 0.015% BAC per hour, so a 0.08% BAC takes roughly 5 hours to reach zero. Coffee and cold showers do not help.
Can I use this to know if I can drive?
No. It is an estimate and impairment begins well below the legal limit. Do not drive after drinking.
Sources
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