📖 What Is BAC?
Blood Alcohol Concentration explained
Blood Alcohol Concentration (BAC) is the percentage of alcohol (ethanol) in the bloodstream, measured in grams per 100 mL of blood (g/dL). A BAC of 0.08% means there are 0.08 grams of alcohol for every 100 mL of blood — the most common legal driving limit worldwide.
BAC rises as alcohol is absorbed into the bloodstream and falls as the liver metabolises it. The rate of rise and fall depends on body weight, sex, food intake, the quantity of alcohol consumed, and more.
🧮 The Widmark Formula
The medically accepted model used worldwide since the 1930s
🔢 Step-by-Step Calculation
How we compute your result
Convert Weight to Pounds
If you enter your weight in kilograms, it is multiplied by 2.20462 to convert to pounds, as the Widmark formula requires weight in pounds.
Calculate Total Alcohol in Ounces
The number of drinks is multiplied by the grams of alcohol per drink, then divided by 28.3495 to convert from grams to ounces of pure ethanol.
Apply Distribution Ratio (r)
Biological males have an r value of 0.73 and females 0.66. This reflects the different proportions of body water, since alcohol distributes evenly through water in the body. Women typically have a lower body-water percentage, resulting in a higher BAC for the same amount of alcohol.
Subtract Metabolised Alcohol
The liver eliminates alcohol at approximately 0.015% BAC per hour. This is multiplied by the number of hours since drinking began and subtracted from the raw BAC. The result cannot go below zero.
Display Result & Status
The final estimated BAC is categorised into effect levels (sober → life-threatening), compared against the common 0.08% legal limit, and the time to full sobriety is calculated.
🍺 What Is a Standard Drink?
One standard drink = 14 grams of pure ethanol (used as the default in our calculator)
| Beverage | Volume | ABV | Alcohol (g) | Standard Drinks |
|---|---|---|---|---|
| 🍺 Regular Beer | 355 mL / 12 oz | 5% | ~14 g | 1.0 |
| 🍷 Table Wine | 148 mL / 5 oz | 12% | ~14 g | 1.0 |
| 🥃 Spirits / Liquor | 44 mL / 1.5 oz | 40% | ~14 g | 1.0 |
| 🍺 Craft / Strong Beer | 355 mL / 12 oz | 8% | ~22 g | ~1.6 |
| 🍷 Fortified Wine | 88 mL / 3 oz | 17% | ~14 g | 1.0 |
| 🍹 Large Cocktail | varies | varies | 20–40 g | 1.5–3.0 |
Adjust Grams per Drink
For cocktails, craft beers, or mixed drinks, increase the "Alcohol per Drink" value in the calculator above the default 14 g for a more accurate estimate.
🔬 Factors That Affect BAC
Why two people can have very different BAC levels after drinking the same amount
Body Weight
Heavier individuals have more body water to dilute alcohol, resulting in lower BAC for the same intake.
Biological Sex
Females typically have less body water and different enzyme activity, leading to higher BAC per unit of alcohol.
Food Intake
Eating before or while drinking slows alcohol absorption significantly and lowers peak BAC.
Drinking Speed
Consuming drinks quickly raises BAC faster than the liver can process, leading to a higher peak.
Genetics & Tolerance
Genetic factors influence enzyme efficiency. Regular drinkers may feel less impaired at the same BAC.
Medications
Many drugs interact with alcohol, amplifying effects or slowing metabolism. Always check with your doctor.
Fatigue & Health
Tiredness, dehydration, and illness can all intensify the effects of alcohol at any given BAC level.
Age
Older adults generally have less body water and slower metabolism, which increases BAC and intensifies effects.
📋 Calculator Limitations
What this calculator cannot account for
This is an Estimate Only
The Widmark formula provides a mathematical approximation. Real-world BAC can vary by ±20–30% from this estimate. Never use this calculator to decide whether it is safe or legal to drive.
- Does not account for food consumption timing or type
- Assumes a fixed metabolic rate of 0.015% per hour (varies between 0.010%–0.020%)
- Does not consider medication interactions
- Does not reflect individual enzyme differences (ADH/ALDH variation)
- Cannot measure actual physical impairment level
- Legal limits may differ from the 0.08% common standard used here
Ready to try it?
Go to the BAC Calculator → or learn about safety and legal limits →