Blood Alcohol Content (BAC) Calculator
This Blood alcohol content (BAC) calculator estimates a person's BAC based on their alcohol intake. If you already have a BAC before you start drinking, you can estimate it based on your drink history and add it to the current calculation. To use this calculator, simply provide your body weight, sex, the time since your first drink, and the amount of alcohol consumed, then click the 'Calculate' button. The result will also provide the time needed for the calculated BAC to drop to 0% or within various legal limits. Click here to find the BAC threshold after which driving becomes illegal in your country. Note that just because you are under the calculated threshold and it is legal to drive does not mean that it is safe to drive. Alcohol affects people differently and the BAC calculation is only an estimate.
This calculator is based on a model developed by Swedish professor Erik Widmark in the 1920s. Due to its limitations, the calculation results are only estimates and are not meant to be precise. Some studies have found that the real BAC of 72% of people is within ±15% of the calculation result. This is a relatively large range, so just because the calculator estimates that your BAC is below the legal limit does not mean that you will necessarily test below the limit with a breathalyzer. If you want to be safe, consider adding at least 20% to the calculated value to have a buffer.
What is BAC?
Blood alcohol content (BAC) measures the amount of alcohol in a person's bloodstream. It is usually expressed as a percentage. For example, a BAC of 0.08% indicates that there are 0.08 grams of alcohol per 100 milliliters of blood. It is a measure of how intoxicated a person is and can be crucial for both medical and legal reasons.
BAC is important because it directly affects a person's ability to perform tasks, particularly those that require concentration and coordination, such as driving. Higher BAC levels can lead to impaired judgment, slower reaction times, and decreased motor skills, significantly increasing the risk of accidents and injuries. Most countries have legal BAC limits for drivers to ensure safety on the roads. In the United States, for example, the legal limit for drivers over 21 years old is typically 0.08%. For commercial drivers, this limit is even lower at 0.04%. Wikipedia has a summary of the legal BAC limits for driving in different countries.
How is BAC measured?
BAC can be measured in several ways. The most common methods include the use of a breathalyzer, blood tests, and sometimes urine tests.
Blood Tests: Blood tests provide the most accurate measure of BAC. A blood sample is taken and analyzed to determine the exact amount of alcohol present. This method is often used in medical settings or when precise measurements are required.
Breath Tests: Breathalyzers are commonly used by law enforcement to measure BAC quickly. These devices estimate BAC by measuring the amount of alcohol in the breath. Although convenient, they may not always be as accurate as blood tests.
Urine Tests: Urine tests can also be used to measure BAC, but they are less accurate than blood or breath tests. These tests measure the amount of alcohol that has passed through the body and can provide an estimate of BAC.
How is BAC calculated?
There are many factors that impact BAC including age, food consumption before drinking, sex, weight, genetics, the type of drink consumed, and more. This calculator uses a formula developed by Swedish professor Erik Widmark in the 1920s to estimate BAC. It is the most widely adopted formula used for measuring BAC and is based on a person's body weight, sex, and the time at which alcohol was consumed. The formula is expressed as follows:
| BAC = |
|
– βT |
Example: John, a man weighing 180 pounds, drank four cups of beer over a period of 3 hours. Each cup contained 330 ml of 5% alcohol beer. What is his BAC after the drinks?
John drank four beers: 4 × 13 = 52 grams of alcohol.
John's weight (W): 180 pounds = 81.6 kg.
Volume of distribution (Vd): 81.6 kg × 0.71 L/kg = 57.9 L.
| BAC = |
|
– βT | |||
| = |
|
– 0.015 × 3 | |||
| = | 0.045% | ||||
So, John's BAC is approximately 0.045%.
Factors impacting BAC
Understanding BAC is crucial for making informed decisions about alcohol consumption and ensuring safety, particularly when it comes to activities like driving. Our calculator, based on the Widmark Formula, can quickly estimate BAC levels using simple information. However, there are many other factors not included in the Widmark formula that impact BAC. Some of these include body weight, sex, time since alcohol consumption, and the amount of alcohol consumed. Below are a few examples:
- Rate of Consumption: Drinking alcohol quickly can lead to higher BAC levels, as the body has less time to metabolize it.
- Food Intake: Eating food before or while drinking can slow the absorption of alcohol into the bloodstream, leading to a lower BAC.
- Age: As people age, their bodies generally become less efficient at metabolizing alcohol. Older adults may experience higher BAC levels and prolonged effects from the same amount of alcohol compared to younger individuals.
All these factors not included in the Widmark Formula contribute to inaccuracies in the calculation. The Widmark Formula is most accurate when used to estimate BAC a few hours after drinking a single dose of alcohol in a fasted state, and it can be within ±20% of the true value. It is not accurate for BAC levels below 0.02% or when alcohol is consumed with food. When using the calculator, please keep the possible error range in mind.
BAC differences in men and women
It is worth noting that alcohol does not impact men and women equally. The observable difference in impact on BAC is largely due to differences in body composition, with women generally having a higher body fat percentage. As a result, given that a man and woman weigh the same, are the same height, and drink the same amount of alcohol, the woman's BAC will be slightly higher. Along with all the other factors described above, this adds to the inaccuracy of BAC estimates. Also, it is more reason that alcohol consumption should not directly be compared between people, since so many factors can impact how alcohol will affect each person.
Impact of various BAC levels
0.0%—Not intoxicated.
0.02%—This is the lowest intoxication level. A person with this BAC may feel relaxed and their judgment may be mildly altered.
0.05%—A person with this BAC may have exaggerated movements and may be louder with some loss of control of small muscles. They may also have blurry vision.
0.08%—This is the legal limit in most US states and is the level at which it is illegal and is considered unsafe for a person to drive.
0.10%—A person with this BAC will likely have reduced reaction time, slurred speech, reduced reasoning capacity, and loss of bodily coordination.
0.15%—This is a high BAC and a person with this BAC likely has little control over their muscles and balance.
0.20-0.29%—A person with this BAC is likely to exhibit confusion, nausea, vomiting, and is at risk of choking due to an impaired gag reflex. They may also experience blackouts.
0.30-0.39%—A person with this BAC may be unconscious and is likely to experience increased heart rate, irregular breathing, loss of bladder control, loss of understanding of their surroundings. They are also at risk of death.
0.40% and over—A person with this BAC is at risk of coma or sudden death due to cessation of their heart or breathing.
Typical drinks and their estimated alcohol content
Below are some standard alcohol drinks and their estimated alcohol content:
| Alcoholic beverage | Alcohol by volume |
|---|---|
| Beer | 4-6% |
| Wine | 5.5-16% |
| Sake | 15% |
| Soju | 14-45% |
| Vodka | 35-95% |
| Rum | 37.5-80% |
| Mezcal, tequila | 32-60% |
| Gin | 37.5%-50% |
| Fernet | 39-45% |
| Arak | 60-65% |