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Widmark Formula
BAC Calculator: Estimate Your Blood Alcohol Content and Time to Sober
Enter your weight, gender, drinks and time to get your estimated BAC, driving verdict, and time until sober.
Step 1 — Select your country
Step 2 — Your details
Step 3 — Tap your drinks
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Blood Alcohol Content
Your estimated BAC is below the legal limit for your selected country.
Add drinks above to see effects.
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Time until BAC reaches zero
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Time until below legal limit
Drinks consumed
0
standard drinks
Legal limit
0.05%
Thailand
What Is BAC and What Does Your Number Mean?
Blood alcohol content (BAC) is the concentration of alcohol in your bloodstream, expressed as grams of alcohol per 100ml of blood. A BAC of 0.08% means there are 0.08 grams of alcohol per 100ml of blood. Even small increases in BAC produce measurable impairments in judgement, reaction time, and coordination — often before the person drinking notices any change.
| BAC level | Typical effects | Legal to drive? |
|---|---|---|
| 0.01% to 0.03% | Mild relaxation, slight warmth | Yes (most countries) |
| 0.04% to 0.06% | Reduced inhibition, mild impairment of judgement | Yes (most countries, but impaired) |
| 0.07% to 0.09% | Impaired coordination, slowed reaction time, reduced memory | Illegal in US (0.08%), Australia (0.05%) |
| 0.10% to 0.15% | Significant impairment, poor balance, slurred speech | Illegal everywhere |
| 0.16% to 0.30% | Severe impairment, possible blackout, vomiting risk | Illegal, dangerous |
| Above 0.30% | Risk of unconsciousness, alcohol poisoning, death | Medical emergency |
How Long Does It Take for Alcohol to Leave Your System?
The liver metabolises alcohol at approximately 0.015% BAC per hour regardless of coffee, water, food, or sleep. This rate is fixed by enzyme kinetics and cannot be meaningfully accelerated. One standard drink raises BAC by approximately 0.02% to 0.03% in most adults, depending on weight and sex.
Three practical examples: a person with a BAC of 0.08% takes approximately 5 hours and 20 minutes to reach zero. A person with 0.15% BAC takes approximately 10 hours. A person who reached 0.20% at midnight will not reach zero until approximately 1pm the following day. Nothing speeds this up.
The only thing that lowers BAC is time. Coffee, water, food, and sleep do not speed up alcohol metabolism. If you have been drinking, the safest choice is always to wait.
Drink Drive Limits by Country
Legal BAC limits vary by country and driver category. The calculator above shows your estimated BAC against the limit for your selected region.
| Country / Region | Legal BAC limit | Zero tolerance applies to |
|---|---|---|
| United States | 0.08% | Commercial drivers (0.04%), under-21 drivers (0.00% to 0.02%) |
| United Kingdom | 0.08% England/Wales/NI, 0.05% Scotland | Professional drivers |
| Australia | 0.05% | Learner and P-plate drivers (0.00%) |
| European Union (most) | 0.05% | Professional and novice drivers (0.02% or 0.00%) |
| Thailand | 0.05% | All drivers |
What Factors Affect Your BAC?
Body weight is the primary factor: alcohol distributes through total body water, so heavier individuals reach lower peak BAC for the same amount of alcohol. Sex differences are significant because women generally have lower total body water as a percentage of body weight and lower gastric alcohol dehydrogenase (ADH) activity, meaning the same intake produces a higher BAC. Food slows gastric emptying and delays peak BAC but does not significantly reduce total alcohol absorbed once drinking is complete. Age matters: older adults tend to have lower total body water and reduced hepatic enzyme activity, producing higher BAC and slower clearance. Certain medications potentiate alcohol including benzodiazepines, antihistamines, and some antibiotics. Genetic variants also play a role: ALDH2 deficiency, common in East Asian populations, impairs acetaldehyde metabolism and produces elevated health risks even at lower consumption levels.
Clinical insight: Patients at Phuket Island Rehab frequently underestimate how long alcohol remains active in their system. A person who drinks heavily at midnight may still have a measurable BAC at 10am the following morning. — John A. Smith, Medical Professional and Addiction Counselor, Phuket Island Rehab.
When Does Drinking Become a Problem?
If someone is using a BAC calculator regularly to decide whether it is safe to drive, or finds they are consistently drinking to levels above 0.08%, that pattern warrants attention. The DSM-5 defines alcohol use disorder across mild, moderate, and severe presentations based on 11 criteria including failed attempts to cut down, continued drinking despite consequences, and cravings that interfere with daily life.
Phuket Island Rehab works with people across the full spectrum of alcohol use, from early-stage concern to severe dependence. Residential treatment in Thailand offers a private, structured environment away from the triggers of daily life. Assessment is confidential and without obligation.
If you are concerned about your drinking or someone else’s, confidential help is available. Phuket Island Rehab: phuketislandrehab.com | SAMHSA National Helpline: 1-800-662-4357 (US, free, 24/7) | 988 Suicide and Crisis Lifeline: call or text 988.
Concerned About Your Drinking?
Phuket Island Rehab offers free, confidential consultations for people who are worried about their alcohol use. No pressure, no obligation.