Blood Alcohol Calculator – Estimate Your BAC
Calculate your Blood Alcohol Content (BAC) based on drinks consumed, body weight, and time. Know when it's safe to drive.
How BAC is Calculated: The Widmark Formula
Blood Alcohol Concentration (BAC) measures the percentage of alcohol in your bloodstream. The Widmark formula estimates BAC: BAC = (Alcohol grams) / (Body weight in grams × r) − (elimination rate × time). The 'r' factor is 0.68 for men and 0.55 for women, reflecting differences in body water distribution. Elimination rate: ~0.015 BAC per hour.
Example: A 70 kg man drinks 3 standard US drinks (42g alcohol) in 2 hours: BAC = (42 / (70000 × 0.68)) × 100 − (0.015 × 2) ≈ 0.088% − 0.03% = 0.058%.
Critical: only time metabolizes alcohol. Coffee, food, water, and exercise do NOT lower BAC faster.
BAC Effects Reference Table
How BAC level affects behavior and physiology:
| BAC (%) | Typical Effects | Legal Driving Status |
|---|---|---|
| 0.01–0.03 | Subtle relaxation, slight mood elevation. Minimal impairment. | Legal (most countries) |
| 0.04–0.06 | Relaxed, impaired judgment begins, reduced reaction time | Legal to drive |
| 0.07–0.09 | Impaired balance, reaction time, coordination and reasoning | Illegal to drive (US: 0.08%) |
| 0.10–0.12 | Significant impairment, slurred speech, poor coordination | Illegal |
| 0.13–0.15 | Gross motor impairment, blurred vision, poor balance | Illegal |
| 0.16–0.20 | Nausea, severe disorientation, marked dysphoria | Illegal |
| 0.25–0.30 | Stupor, very limited awareness, loss of consciousness risk | Medical emergency risk |
| 0.30+ | Coma risk, respiratory depression. Life-threatening. | Emergency — call for help |
Factors That Affect BAC
Many variables affect how quickly alcohol is absorbed and how high BAC peaks:
- Body weight and composition: More body weight = more body water = lower BAC per drink. Fat tissue has lower water content than muscle, so body composition matters. Two people of equal weight but different body fat percentages will reach different BAC levels.
- Sex: Women typically reach higher BAC than men for equivalent consumption due to lower total body water, different enzyme levels (less gastric alcohol dehydrogenase), and hormonal factors affecting absorption rate.
- Food: A full stomach slows alcohol absorption by up to 50%, reducing peak BAC and delaying it by 30–90 minutes. Drinking on an empty stomach raises BAC significantly faster and higher.
- Drinking rate: Faster consumption produces higher peak BAC because absorption rate exceeds elimination rate.
- Tolerance: Tolerance affects perceived effects but does NOT change the BAC level or the rate of alcohol metabolism. Tolerant drinkers feel less impaired at the same BAC — but are equally impaired physiologically.
- Medications: Many medications interact with alcohol to amplify effects or alter absorption.
Alcohol and Athletic Performance
For runners and athletes, even moderate alcohol consumption has documented performance consequences:
- Sleep disruption: Alcohol falls asleep faster but fragments REM sleep and reduces sleep quality in the second half of the night. Poor sleep degrades next-day running performance, recovery, and adaptation to training.
- Muscle protein synthesis: Consuming alcohol post-exercise reduces MPS (muscle protein synthesis) by up to 37% even at social drinking quantities (Parr et al., 2014, Medicine & Science in Sports & Exercise). This impairs muscle repair after hard sessions.
- Dehydration: Alcohol suppresses anti-diuretic hormone (ADH), increasing urine output and causing net dehydration. Even moderate drinking the night before a race or long run can meaningfully impair performance through reduced hydration status.
- Glycogen synthesis: Alcohol consumed post-exercise interferes with muscle glycogen replenishment, slowing recovery from glycogen-depleting workouts.
Evidence-based guidance: avoid alcohol within 24 hours of key training sessions or races. Occasional light social drinking has minimal long-term impact on recreational runners; regular heavier drinking progressively impairs training quality and recovery.
Standard Drink Sizes and Unit Equivalents
Different countries define 'standard drinks' differently, which causes significant confusion when following health guidelines:
| Country | Standard Drink Contains | Equivalent |
|---|---|---|
| United States | 14g pure alcohol | 355ml beer (5%), 148ml wine (12%), 44ml spirits (40%) |
| United Kingdom | 8g pure alcohol (1 unit) | 25ml spirits, 76ml wine, 250ml low-strength beer |
| Australia | 10g pure alcohol | 285ml beer (4.9%), 100ml wine (13%), 30ml spirits (40%) |
| Europe (general) | 10–12g pure alcohol | Varies by country |
When following guidelines like 'no more than 2 drinks per day,' verify which standard drink definition applies. A US standard drink (14g) is equivalent to 1.75 UK units or 1.4 Australian standard drinks.
How Long to Sober Up: Time Calculation
The liver eliminates alcohol at a fixed rate of approximately 0.015% BAC per hour regardless of food, coffee, exercise, or sleep. To calculate when BAC returns to zero: Time (hours) = Peak BAC ÷ 0.015.
Examples:
| Peak BAC | Hours to Sober (BAC = 0) | Time if Peak at Midnight |
|---|---|---|
| 0.05% | 3.3 hours | 3:20 AM |
| 0.08% | 5.3 hours | 5:20 AM |
| 0.10% | 6.7 hours | 6:40 AM |
| 0.15% | 10.0 hours | 10:00 AM |
| 0.20% | 13.3 hours | 1:20 PM next day |
Important for runners: even if BAC is technically zero in the morning, residual effects on dehydration and sleep quality from heavy drinking the previous evening can meaningfully impair performance. Plan race days and key training sessions around social drinking accordingly.
Frequently Asked Questions
How is BAC calculated?
Using the Widmark formula: BAC = (grams of alcohol consumed) / (body weight in grams × distribution factor) × 100 − (elimination rate × hours drinking). Distribution factor: 0.68 for men, 0.55 for women. Elimination rate: ~0.015% BAC per hour. Our calculator applies this formula automatically.
How long does it take to sober up?
Alcohol is eliminated at approximately 0.015% BAC per hour. Divide your peak BAC by 0.015 for hours to sobriety. BAC 0.10%: ~6.7 hours. BAC 0.08%: ~5.3 hours. Nothing speeds this — not coffee, food, water, exercise, or sleep. Only time metabolizes alcohol.
Can I run after drinking alcohol?
Not advisable for performance or safety reasons. Alcohol impairs reaction time, coordination, and thermoregulation. It causes dehydration and disrupts recovery. For serious training, avoid alcohol within 24 hours of hard sessions. Light drinking the night before an easy recovery jog has minimal impact but reduces training quality.
Does eating before drinking lower BAC?
Eating BEFORE or WHILE drinking slows alcohol absorption by up to 50% compared to drinking on an empty stomach, resulting in lower peak BAC and a more gradual rise. Eating AFTER you've already consumed significant alcohol has minimal effect on the alcohol already in your bloodstream.
What BAC level is legally drunk?
US: 0.08% for most adults (0.02% for drivers under 21 in some states). UK/Australia: 0.08%. Most of Europe: 0.05%. Japan/China: 0.03%. Sweden/Norway: 0.02%. UAE/Saudi Arabia: 0.00% (zero tolerance). All of these are the legal DRIVING limits; the term 'legally drunk' specifically refers to driving impairment thresholds.
Why do women reach higher BAC than men?
Three main reasons: (1) Women have proportionally more body fat and less body water — alcohol distributes in water, so less water = less dilution; (2) Women have lower levels of gastric alcohol dehydrogenase, the stomach enzyme that starts breaking down alcohol before absorption; (3) Hormonal variations across the menstrual cycle affect alcohol metabolism rate.
What is a standard drink?
In the US: 14g pure alcohol = 355ml regular beer (5% ABV), 148ml wine (12% ABV), or 44ml spirits (40% ABV). In the UK: 8g = 1 unit = 25ml spirits or 76ml wine. In Australia: 10g = 1 standard drink = 285ml regular beer. Always check which definition is being used when following drinking guidelines.
BAC Levels and Effects
Blood Alcohol Concentration (BAC) effects at different levels. Always arrange safe transport if you have consumed alcohol.
| BAC (g/dL) | Stage | Typical Effects |
|---|---|---|
| 0.01–0.05 | Subclinical | Normal behavior; slight warmth; relaxation |
| 0.06–0.10 | Impairment begins | Mild euphoria; lowered inhibitions; slower reaction time |
| 0.11–0.15 | Clear impairment | Impaired coordination; slurred speech; legal DUI in most countries |
| 0.16–0.20 | Serious impairment | Poor balance; nausea; serious motor impairment |
| 0.21–0.29 | Severe impairment | Significant coordination loss; blackout possible |
| 0.30–0.39 | Danger zone | Loss of consciousness; breathing depression; life-threatening |
| 0.40+ | Potentially fatal | Coma; respiratory failure; death possible |