Free BAC calculator · Widmark and Watson formulas
Blood Alcohol Calculator: Estimate Your BAC and Sober Time
A blood alcohol calculator estimates your blood alcohol concentration (BAC) from your body weight, sex, drinks and the time since your first drink. One US standard drink holds 14 grams of pure alcohol and raises BAC by about 0.028% in a 160 lb (73 kg) man. The body then clears about 0.015% per hour, so a BAC of 0.08% takes about 5 hours 20 minutes to reach 0.00%.
Last verified
14 g
Pure alcohol in one US standard drink: 12 oz of beer, 5 oz of wine or 1.5 oz of spirits.
Source: NIAAA
0.015%
Average drop in BAC per hour. Coffee, water and cold showers do not speed it up.
Source: BMJ, Paton 2005
44 min
Average gap between US drunk-driving deaths in 2024. That is 11,904 lives in one year.
Source: NHTSA
Free BAC calculator
What is my blood alcohol level right now?
Enter your weight, sex and drinks. You get your estimated BAC, the time you drop below your legal limit and the time you reach 0.00%. Nothing you type leaves your device.
Estimated BAC
—%
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Waiting for your details
The vertical line marks your legal limit.
Enter your weight, sex and drinks to see your estimate.
- Below your limit
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- Back to 0.00%
- —
- Alcohol consumed
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- Formula
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This level can be life-threatening. If someone is confused, vomiting, breathing slowly or hard to wake, call emergency services now.
Estimate only. Food, medication, health and drinking pace change your real BAC, and it can keep rising after your last drink. Never use this result to decide whether to drive.
BAC chart
What do BAC levels mean?
Each BAC level brings predictable effects. Driving skills drop from 0.02%, and most countries ban driving at 0.05% or 0.08%.
| BAC | Common effects | Driving | Time to 0.00% |
|---|---|---|---|
| 0.02% | Relaxation, mild loss of judgment, weaker multitasking. | Illegal in zero-tolerance places | 1 h 20 min |
| 0.05% | Lower alertness, reduced coordination, slower response to hazards. | Over the limit in most of Europe | 3 h 20 min |
| 0.08% | Poor muscle control, worse reasoning, weaker speed control. | Illegal in all US states | 5 h 20 min |
| 0.10% | Slurred speech, slow reactions, poor lane keeping. | Clearly impaired | 6 h 40 min |
| 0.15% | Major loss of balance, vomiting possible, blackouts start near 0.16%. | Severe crash risk | 10 h |
| 0.30%+ | Confusion, stupor, risk of alcohol poisoning and death. | Medical emergency | 20 h or more |
Time to 0.00% assumes the average clearance rate of 0.015% per hour. Slow metabolisers can take 50% longer.
Drinks to the limit
How many drinks put you at 0.08%?
A 160 lb man reaches 0.08% after about 2.8 standard drinks taken quickly. Lighter people and women get there sooner, because they have less body water to dilute the alcohol.
1.7
120 lb woman
Standard drinks to peak at 0.08%.
2.3
160 lb woman
Standard drinks to peak at 0.08%.
2.8
160 lb man
Standard drinks to peak at 0.08%.
3.5
200 lb man
Standard drinks to peak at 0.08%.
Calculated with the Widmark formula (r = 0.68 men, 0.55 women), no time elapsed. One standard drink is 14 g of alcohol: 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits.
Sobering up
How long does it take to sober up?
Your liver clears about one standard drink per hour, which lowers BAC by about 0.015% per hour. Nothing speeds this up.
Rule 1
1 / hr
One drink per hour
Drinking faster than this makes BAC climb.
Rule 2
90 min
Peak comes later
BAC can keep rising 30 to 90 minutes after your last drink.
Rule 3
0%
No shortcuts
Coffee, showers and exercise do not lower BAC.
Rule 4
8 h+
Morning after
A 0.12% night out can leave you over 0.00% at breakfast.
How long until I can drive after drinking?
Divide the gap between your BAC and your legal limit by 0.015. At 0.11% with a 0.08% limit, that is 0.03 / 0.015 = 2 hours. At 0.11% with a 0.05% limit, it is 4 hours. The safest choice is to wait until 0.00%.
The maths
How is BAC calculated?
This calculator uses the Widmark formula by default. Add your age and height and it switches to the Watson total body water formula.
What is the Widmark formula?
Widmark (1932)BAC % = A / (W × r × 10) − β × t
- A
- Alcohol in grams. Volume ml × ABV % × 0.00789.
- W
- Body weight in kg.
- r
- Body water ratio. 0.68 men, 0.55 women.
- β
- Clearance rate. 0.015% per hour average.
- t
- Hours since your first drink.
What is the Watson formula?
Watson TBW, menTBW = 2.447 − 0.09516 × age + 0.1074 × height cm + 0.3362 × weight kg
Watson TBW, womenTBW = −2.097 + 0.1069 × height cm + 0.2466 × weight kg
BAC from TBWBAC % = (A × 0.08 / TBW) − β × t
Blood is about 80% water, so the 0.08 factor converts body water to blood. Watson fits tall, short, older and very muscular people better than a fixed r.
Worked example: a 160 lb (72.6 kg) man drinks 3 beers (3 × 14 g = 42 g) over 2 hours. BAC = 42 / (72.6 × 0.68 × 10) − 0.015 × 2 = 0.085 − 0.030 = 0.055%.
Legal limits
What is the legal BAC limit in my country?
The US, Canada, England and Wales use 0.08%. Most of Europe and Australia use 0.05%. Many countries set 0.02% or less for new and professional drivers.
| Country | Limit | New / pro |
|---|---|---|
| USA | 0.08% (Utah 0.05%) | 0.04% commercial |
| Canada | 0.08% | 0.00% most provinces |
| England, Wales | 0.08% | 0.08% |
| Scotland | 0.05% | 0.05% |
| Greece | 0.05% | 0.02% |
| Germany | 0.05% | 0.00% |
| Australia | 0.05% | 0.00% |
| Japan | 0.03% | 0.03% |
| Sweden, Norway | 0.02% | 0.02% |
| Hungary, Czechia | 0.00% | 0.00% |
Europe states limits in g/L. Divide by 10 to get BAC %: 0.5 g/L equals 0.05%.
FAQ
Blood alcohol questions, answered
Short, direct answers to the questions people ask most about BAC.
How accurate is a blood alcohol calculator?
A blood alcohol calculator gives an estimate that can be off by 20% or more. Food, medication, liver health and drinking pace all change your real BAC. Only a breath or blood test measures it.
Does eating food lower my BAC?
Eating before drinking slows absorption and lowers your peak BAC, but it does not remove alcohol. Food eaten after drinking has little effect.
Why do women reach a higher BAC than men?
Women reach a higher BAC from the same drinks because they have less body water on average. The Widmark ratio is 0.55 for women and 0.68 for men, so the same drink gives about 24% higher BAC.
What does BAC 0.08% mean?
A BAC of 0.08% means 0.08 grams of alcohol per 100 ml of blood, which equals 0.8 g/L or 0.8‰. It is the legal driving limit in the US.
Can I use this calculator to decide if I can drive?
No. Use it to understand how alcohol affects you, not to decide whether to drive. If you have been drinking, use a taxi, a ride share or a sober driver.
Sources
Which sources does this calculator use?
Every number on this page comes from a government agency or peer-reviewed research.
Last verified
This page is for education only. It is not medical or legal advice. If someone shows signs of alcohol poisoning, such as slow breathing, blue skin or being hard to wake, call emergency services.
Plan ahead
Know your number before your next drink
Check your estimate in 30 seconds. Then book the ride home before you need it.