BAC Calculator
Never use this to decide whether it is safe to drive. The only safe level for driving is zero. Results are rough estimates; real blood alcohol varies with food, medication, health and many other factors.
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Results
Estimated BAC 0.075% 2 h after the first drink (42 g of alcohol, 160 lb). Never use this to decide whether it is safe to drive. The only safe level for driving is zero.
Never use this to decide whether it is safe to drive. The only safe level for driving is zero. This is a rough estimate. Real BAC varies with food, medication, health, drinking speed, genetics and many other factors, and it can keep rising after your last drink while alcohol is still being absorbed.
This is not medical or legal advice. If you are worried about your drinking, talk to a doctor.
How to use the BAC calculator
- Choose your sex and enter your weight in pounds or kilograms.
- Enter what you drank as US standard drinks, UK units, or the size and strength (ABV) of each drink.
- Enter the hours since your first drink. The result is an estimate for this moment, with the approximate time until it reaches 0.00%.
BAC formula
r = 0.68 for men, 0.55 for women; β ≈ 0.015% per hour
Alcohol (g) = volume (mL) × ABV ÷ 100 × 0.789
Hours to 0.00% = current BAC ÷ β
Swedish chemist Erik Widmark published this formula in 1932. Alcohol spreads through the body's water, so the same amount gives a higher concentration in a smaller body or one with less water; the ratio r captures that, and is lower on average for women. The body then removes alcohol at a roughly steady rate. A 2010 review by A. W. Jones found 0.015% per hour a good average for moderate drinkers, with a range of about 0.010 to 0.035% per hour between people. A US standard drink holds 14 g of pure alcohol (NIAAA); a UK unit is 8 g, or 10 mL (NHS).
Worked example
A woman who weighs 140 lb (63.5 kg) has three US standard drinks, 42 g of alcohol. Before any is removed, the formula gives 42 ÷ (63,503 × 0.55) × 100 = 0.120%. Two hours after her first drink it estimates 0.120 − 2 × 0.015 = 0.090%, and roughly another 6 h 1 min to reach zero, or 9 h 2 min if her body clears alcohol more slowly. Her real level could be noticeably higher or lower. Never use this to decide whether it is safe to drive. The only safe level for driving is zero.
Alcohol in common drinks
| Drink | Pure alcohol | US standard drinks | UK units |
|---|---|---|---|
| Beer, 12 fl oz at 5% | 14 g | 1 | 1.8 |
| Wine, 5 fl oz at 12% | 14 g | 1 | 1.8 |
| Spirits, 1.5 fl oz at 40% | 14 g | 1 | 1.8 |
| Beer, UK pint (568 mL) at 4% | 17.9 g | 1.3 | 2.3 |
| Beer, 330 mL bottle at 5% | 13 g | 0.9 | 1.7 |
| Wine, 175 mL glass at 12% | 16.6 g | 1.2 | 2.1 |
| Wine, 250 mL glass at 13% | 25.6 g | 1.8 | 3.3 |
| Spirits, 25 mL at 40% | 7.9 g | 0.6 | 1 |
Drinks poured at home or in bars are often larger or stronger than these examples, so check the ABV on the label.
How long it takes to reach zero
Only time lowers BAC. Coffee, a cold shower or walking it off will not sober you up, as NIAAA points out.
| BAC | At 0.015% an hour (average) | At 0.010% an hour (slower) |
|---|---|---|
| 0.020% | 1 h 20 min | 2 h |
| 0.050% | 3 h 20 min | 5 h |
| 0.080% | 5 h 20 min | 8 h |
| 0.100% | 6 h 40 min | 10 h |
| 0.150% | 10 h | 15 h |
| 0.200% | 13 h 20 min | 20 h |
Legal limits, for information
These are the legal limits for most drivers. They are not a target: NHTSA's guide The ABCs of BAC describes effects on driving, such as reduced visual function and difficulty doing two things at once, from 0.02%, and this calculator cannot tell you what your real level is. Many places also set lower limits for new, young or commercial drivers.
| Where | Limit for most drivers |
|---|---|
| United States (all states except Utah) | 0.08 g/dL (0.08%) |
| Utah | 0.05 g/dL (0.05%) |
| England, Wales and Northern Ireland | 80 mg per 100 mL of blood |
| Scotland | 50 mg per 100 mL of blood |
Why your real BAC may differ
- Food and drinking speed. Drinking on an empty stomach or quickly raises BAC faster and higher.
- Absorption takes time. The formula assumes all alcohol is absorbed at once; in reality BAC can keep rising after your last drink.
- Body and health. Body composition, age, liver health, genetics and medicines all change how alcohol is handled. Some medicines interact dangerously with alcohol.
- Counting errors. Home and bar pours are often bigger than a standard drink, so it is easy to undercount.
If someone is confused, vomiting, having seizures, breathing slowly or irregularly, has clammy or bluish skin, or cannot be woken, these can be signs of alcohol overdose: call 911 (999 or 112 in the UK) and stay with them. If you are concerned about how much you drink, your doctor can help. This is not medical advice; talk to a doctor or registered dietitian.
Sources
- Widmark EMP. Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. 1932.
- Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Sci Int 2010;200:1–20.
- NIAAA, What is a standard drink? and Understanding the dangers of alcohol overdose.
- NHS, Calculating alcohol units.
- NHTSA, Drunk driving and The ABCs of BAC (2005); GOV.UK, The drink drive limit.
Frequently asked questions
How is blood alcohol concentration estimated?
The Widmark formula divides the grams of alcohol by body weight times a body-water ratio (about 0.68 for men and 0.55 for women), then subtracts about 0.015% for each hour since drinking began. For a 140 lb woman, three US standard drinks (42 g) give about 0.120% before elimination and roughly 0.090% two hours later. Real levels vary widely, and the estimate must never be used to decide whether to drive.
How long does it take for alcohol to leave your body?
On average the body removes about 0.015% BAC an hour, but the range between people is roughly 0.010% to 0.035% an hour. At the average rate, a BAC of 0.08% takes about 5 hours 20 minutes to reach zero, and 8 hours at 0.010% an hour. Coffee, cold showers and walking do not speed this up.
What is a standard drink?
In the US, a standard drink has 14 g of pure alcohol (NIAAA): about 12 fl oz of 5% beer, 5 fl oz of 12% wine or 1.5 fl oz of 40% spirits. In the UK, a unit is 8 g or 10 mL of pure alcohol (NHS), so a pint of 4% beer is about 2.3 units.
Can I use a BAC calculator to know if I can drive?
No. Never use this to decide whether it is safe to drive. The only safe level for driving is zero. A formula cannot measure your real blood alcohol, which depends on food, medication, health and many other factors, and NHTSA describes effects on driving from 0.02%.
Why do women usually reach a higher BAC than men?
On average women have less body water for their weight, so the same alcohol is more concentrated. In the Widmark formula, four standard drinks (56 g) give an estimated 0.160% before elimination for a 140 lb woman and 0.130% for a 140 lb man. These are estimates, not measurements.