BAC Calculator
Estimate your blood alcohol content (BAC) from your weight, sex, the drinks you had and the time since you started drinking, using the Widmark formula.
Results
| Item | Value |
|---|
Estimated BAC over time
| Hours after first drink | Estimated BAC |
|---|
Quick Answer
BAC ≈ alcohol in grams ÷ (body weight in grams × r) × 100 − 0.015 × hours, where r is 0.68 for men and 0.55 for women. A 180 lb man who had four 12 oz beers at 5% two hours ago has an estimated BAC of about 0.071%.
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Table of Contents
- BAC Calculator
- Quick Answer
- Related Calculators
- How This BAC Calculator Works
- How to Use the BAC Calculator
- Core Formulas
- Key Terms
- Worked Example
- Real-Life Examples
- BAC vs Standard Drinks
- US Standard Drink Examples
- What Changes Your BAC
- Common Mistakes to Avoid
- Frequently Asked Questions
- References & Sources
How This BAC Calculator Works
Enter your sex, body weight, how many drinks you had, the size and strength of each drink, and the hours since your first drink. The calculator works out the grams of pure alcohol, spreads it through your body water using the Widmark formula, and subtracts the alcohol your body has removed over time. It also shows how BAC is likely to fall hour by hour.
Quick explanation: BAC is the percent of your blood that is alcohol.
- 0.08%: the legal limit for drivers 21 and over in most states.
- Standard drink: about 14 grams of pure alcohol in the US.
- Time: BAC falls by roughly 0.015% per hour.
How to Use the BAC Calculator
- Choose your sex and enter your body weight.
- Enter how many drinks you had.
- Enter the size of each drink in fluid ounces and its ABV.
- Enter the hours since your first drink.
- Press Calculate and read the estimated BAC and the hourly table.
Core Formulas
- Alcohol (g): drinks × fl oz × ABV × 29.57 mL × 0.789 g/mL
- Peak BAC (%): alcohol (g) ÷ (weight (g) × r) × 100
- r: 0.68 for men, 0.55 for women (Widmark's values)
- BAC now: peak BAC − 0.015 × hours
- Hours to zero: peak BAC ÷ 0.015
Key Terms
- BAC: blood alcohol content, the percent of alcohol in the blood.
- ABV: alcohol by volume, the percent of a drink that is alcohol.
- Standard drink: about 14 grams, or 0.6 fl oz, of pure alcohol in the US.
- Widmark formula: a classic formula to estimate BAC from alcohol, body weight and time.
- Elimination rate: how fast the body removes alcohol, about 0.015% per hour on average.
Worked Example
A 140 lb woman drinks three 5 oz glasses of wine at 12%, and one hour has passed.
- Alcohol = 3 × 5 × 0.12 × 29.57 × 0.789 = 42.0 g
- Peak BAC = 42.0 ÷ (140 × 453.6 × 0.55) × 100 = 0.120%
- BAC now = 0.120 − 0.015 = 0.105%
Real-Life Examples
- Learning: see how fast four beers raise BAC for a 180 lb man: a peak of about 0.101%.
- Drink size: one 16 oz craft beer at 8% holds about 2.1 standard drinks.
- Body weight: the same four beers give a 130 lb man a peak of about 0.140%.
- Planning: it takes hours, not minutes, for alcohol to clear. Plan a ride before you drink.
BAC vs Standard Drinks
- Standard drinks: a way to count alcohol. One is 14 g, such as 12 oz of 5% beer.
- BAC: how much alcohol is in your blood, which depends on your body and time.
- Link: the same number of drinks gives different BAC levels for different people.
US Standard Drink Examples
Source: NIAAA standard drink sizes. The last two rows show common drinks that hold more than one standard drink.
| Drink | Size | ABV | Pure alcohol |
|---|---|---|---|
| Regular beer | 12 fl oz | 5% | 14.0 g |
| Wine | 5 fl oz | 12% | 14.0 g |
| Distilled spirits | 1.5 fl oz | 40% | 14.0 g |
| Craft beer (not standard) | 16 fl oz | 8% | 29.9 g |
| Large wine pour (not standard) | 9 fl oz | 13% | 27.3 g |
What Changes Your BAC
- Food: eating slows how fast alcohol enters the blood.
- Body size and water: more body water means a lower BAC from the same drinks.
- Drinking speed: drinks taken quickly raise BAC faster.
- Drink strength: craft beers and large pours often hold more than one standard drink.
Common Mistakes to Avoid
- Using it to decide whether to drive. It is only an estimate. Do not drive after drinking.
- Counting glasses, not alcohol. A large pour or strong beer can be two standard drinks.
- Thinking coffee or a shower sobers you up. Only time lowers BAC.
- Ignoring the last drinks. BAC can keep rising after you stop as alcohol is absorbed.
- Assuming zero the next morning. After heavy drinking, BAC can still be above zero.
Frequently Asked Questions
With the Widmark formula: grams of alcohol ÷ (body weight in grams × r) × 100, minus 0.015 for each hour.
In the US it is 0.08% or 0.05% depending on the state, and 0.04% for commercial drivers. Drivers under 21 face stricter rules.
It depends on weight, sex and time. Enter your numbers to see an estimate, but remember it is not exact.
On average about 0.015% per hour, so a BAC of 0.08% takes over 5 hours to reach zero.
About 14 grams of pure alcohol, such as 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits.
On average women have less body water for their weight, so the same alcohol is more concentrated.
Food slows absorption and can lower the peak, but it does not remove alcohol.
No. Coffee, water, cold showers and exercise do not speed up how fast your liver removes alcohol.
It is a rough estimate. Real BAC can be higher or lower. Only a breath or blood test measures it.
The share of body weight that holds alcohol. Widmark's values are 0.68 for men and 0.55 for women.
No. Do not use this to decide. Alcohol affects driving below the limit, and the estimate may be wrong.
Add up the ounces and ABV of each spirit in it, or count it as one drink with its total spirit ounces and ABV.
References & Sources
| Source | Used For | Link |
|---|---|---|
| NIAAA, What Is a Standard Drink? | US standard drink is 14 grams of pure alcohol, with common drink sizes. | https://www.niaaa.nih.gov/alcohols-effects-health/what-standard-drink |
| Wikipedia, Blood alcohol content | The Widmark formula, r values and elimination rate. | https://en.wikipedia.org/wiki/Blood_alcohol_content |
| Wikipedia, Drunk driving law by country | US limits of 0.05% or 0.08% by state, and 0.04% for commercial drivers. | https://en.wikipedia.org/wiki/Drunk_driving_law_by_country |