How is BAC calculated?

BAC is calculated using the Widmark Formula: BAC = (Alcohol consumed in grams ÷ (Body weight in grams × r)) × 100 − (0.015 × Hours since drinking began). The 'r' factor is the Widmark distribution constant: 0.68 for males and 0.55 for females (reflecting the higher proportion of body water in males). One US standard drink contains 14 grams of pure alcohol. For example, a 160 lb male (72.6 kg) who drinks 3 beers (42g alcohol) over 2 hours: BAC = (42 ÷ (72,575 × 0.68)) × 100 − (0.015 × 2) = 0.085% − 0.030% = 0.055% BAC.

What is the legal BAC limit for driving in the US?

In 49 US states, the legal BAC limit for drivers aged 21 and over is 0.08% (80 mg/dL). Utah has a stricter limit of 0.05% (50 mg/dL). For commercial drivers (CDL), the federal limit is 0.04% in all states. For drivers under 21, all states have zero-tolerance laws — typically 0.00–0.02%. At BAC 0.08%, the risk of a crash is approximately 7 times higher than at 0.00%. At 0.15%, crash risk is 25 times higher.

How long does it take for BAC to reach zero?

The liver metabolizes alcohol at a constant rate of approximately 0.015% BAC per hour (one standard drink per hour for most adults). To calculate sobriety time: Hours to zero = Current BAC ÷ 0.015. For example, BAC 0.12% takes 0.12 ÷ 0.015 = 8 hours to reach 0.00%. Nothing speeds up this process — not coffee, cold showers, exercise, food, or water. Only time reduces BAC. The 0.015%/hour rate is an average; some individuals metabolize as slowly as 0.010%/hour (slower) or 0.020%/hour (faster).

Why do women have higher BAC than men after the same drinks?

Women achieve higher BAC than men of equal weight after identical alcohol consumption for two reasons: (1) The Widmark 'r' factor is lower for women (0.55) versus men (0.68) because women have proportionally less body water and more body fat — alcohol distributes only in water, not fat. (2) Women have lower levels of alcohol dehydrogenase (ADH), the stomach enzyme that begins breaking down alcohol before it enters the bloodstream. These combined factors mean a 140 lb woman and a 140 lb man drinking the same amount will have meaningfully different BAC levels, with the woman testing higher.

How is BAC calculated?

BAC is calculated using the Widmark Formula: BAC = (Alcohol consumed in grams ÷ (Body weight in grams × r)) × 100 − (0.015 × Hours since drinking began). The 'r' factor is the Widmark distribution constant: 0.68 for males and 0.55 for females (reflecting the higher proportion of body water in males). One US standard drink contains 14 grams of pure alcohol. For example, a 160 lb male (72.6 kg) who drinks 3 beers (42g alcohol) over 2 hours: BAC = (42 ÷ (72,575 × 0.68)) × 100 − (0.015 × 2) = 0.085% − 0.030% = 0.055% BAC.

What is the legal BAC limit for driving in the US?

In 49 US states, the legal BAC limit for drivers aged 21 and over is 0.08% (80 mg/dL). Utah has a stricter limit of 0.05% (50 mg/dL). For commercial drivers (CDL), the federal limit is 0.04% in all states. For drivers under 21, all states have zero-tolerance laws — typically 0.00–0.02%. At BAC 0.08%, the risk of a crash is approximately 7 times higher than at 0.00%. At 0.15%, crash risk is 25 times higher.

How long does it take for BAC to reach zero?

The liver metabolizes alcohol at a constant rate of approximately 0.015% BAC per hour (one standard drink per hour for most adults). To calculate sobriety time: Hours to zero = Current BAC ÷ 0.015. For example, BAC 0.12% takes 0.12 ÷ 0.015 = 8 hours to reach 0.00%. Nothing speeds up this process — not coffee, cold showers, exercise, food, or water. Only time reduces BAC. The 0.015%/hour rate is an average; some individuals metabolize as slowly as 0.010%/hour (slower) or 0.020%/hour (faster).

Why do women have higher BAC than men after the same drinks?

Women achieve higher BAC than men of equal weight after identical alcohol consumption for two reasons: (1) The Widmark 'r' factor is lower for women (0.55) versus men (0.68) because women have proportionally less body water and more body fat — alcohol distributes only in water, not fat. (2) Women have lower levels of alcohol dehydrogenase (ADH), the stomach enzyme that begins breaking down alcohol before it enters the bloodstream. These combined factors mean a 140 lb woman and a 140 lb man drinking the same amount will have meaningfully different BAC levels, with the woman testing higher.

🍺 Widmark Formula · US Legal Limit 0.08% · Forensic BAC Estimation

BAC Calculator — Blood Alcohol Content

Calculate your estimated Blood Alcohol Content using the Widmark Formula. Compare to US legal driving limits, see effects by BAC level, and estimate time until sober. Enter weight, sex, drinks, and hours elapsed.

NM Clinically reviewed byDr. Nikhil Mahajan, PT, MPT · Jan 15, 2025

0.02%Subclinical — most feel no impairment

0.05%Utah legal limit — impairment begins

0.08%Legal limit — 49 US states (21+)

0.04%CDL commercial driver limit

Educational tool only. BAC estimates vary based on individual metabolism, food intake, medications, and health conditions. Do not use this calculator to determine fitness to drive. When in doubt — do not drive. Call a rideshare.

Calculate Your BAC

Biological Sex

♂Maler = 0.68

♀Femaler = 0.55

Widmark r-factor differs by sex due to body water ratio

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Use actual body weight — not ideal weight

Time Since First Drink

hours

Hours elapsed since the first drink of the session

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Custom Drink — Enter alcohol grams directly

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Estimated BAC 0.000%

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Est. Hours to Sober —

BAC Effects Chart — Blood Alcohol Level Guide

BAC Level	Impairment Level	Effects & Symptoms	Driving & Safety
0.020–0.039%	Subclinical	Mild relaxation, slight mood elevation, minor loss of shyness. Most people do not feel impaired.	Minimal effect on most drivers
0.040–0.059%	Mild Impairment	Lowered inhibitions, reduced caution, mild euphoria, slightly slowed reaction time. Judgment beginning to be affected.	Some states consider impaired (Utah 0.05%)
0.060–0.079%	Moderate Impairment	Impaired balance, slurred speech, reduced coordination, poor judgment, slowed reaction time. Memory retrieval affected.	Approaching or at legal limit in most US states
0.080–0.099%	Legal Limit (Most US)	Clearly impaired coordination and reaction time. Poor short-term memory. Difficulty with balance. Dramatically reduced driving ability.	ILLEGAL in all 50 US states. Crash risk 7× higher than sober.
0.100–0.149%	Severe Impairment	Significantly impaired coordination, slurred speech, blurred vision, vomiting possible, severe loss of judgment and control.	Extremely dangerous. Crash risk 25× higher at 0.15%.
0.150–0.199%	Very Severely Impaired	Loss of motor control, confusion, disorientation, possible blackouts. Nausea and vomiting. Major CNS depression.	Cannot drive safely. High accident and fatality risk.
0.200–0.249%	Dangerously Intoxicated	Loss of consciousness possible, unresponsive stupor, choking risk from vomiting, hypothermia risk, breathing slowed.	Unable to drive. Medical emergency risk.
≥ 0.250%	Life-Threatening	Alcohol poisoning. Unconsciousness, respiratory depression, aspiration risk, seizures, potentially fatal. Emergency medical care required.	Medical emergency — call 911 immediately.

Effects vary by individual tolerance, food intake, medications, fatigue, and health status. These are approximate averages from the National Highway Traffic Safety Administration (NHTSA) and published pharmacology literature.

Standard Drink Equivalents — US Reference

Drink Type	Serving Size	ABV	Alcohol (grams)	Standard Drinks
🍺 Regular Beer	12 oz can/bottle	~5%	14g	1 standard drink
🍺 Craft Beer (Strong)	12 oz	~8%	22g	~1.5 standard drinks
🍷 Table Wine	5 oz glass	~12%	14g	1 standard drink
🍷 Fortified Wine	3.5 oz	~17%	14g	1 standard drink
🥃 Shot of Spirits	1.5 oz	~40%	14g	1 standard drink
🍹 Mixed Drink	Varies	Varies	14–28g+	1–2+ standard drinks
🫧 Hard Seltzer	12 oz	~5%	14g	1 standard drink
🍺 Malt Liquor	12 oz	~7%	20g	~1.5 standard drinks

One US standard drink = 14 grams of pure alcohol (NIAAA definition). Many cocktails, craft beers, and large pour wines contain 1.5–3+ standard drinks in a single serving.

BAC Calculator — How Blood Alcohol Content Works

Blood Alcohol Content (BAC) measures the concentration of alcohol in your bloodstream, expressed as a percentage by weight (grams of alcohol per 100 mL of blood). A BAC of 0.08% means 0.08 grams of alcohol per 100 mL of blood — the legal limit for driving in 49 US states. BAC is calculated using the Widmark Formula, the global forensic and clinical standard developed by Erik Widmark in the 1920s: BAC = (Alcohol in grams ÷ (Body weight in grams × r)) × 100 − (0.015 × Hours since first drink).

The Widmark r-Factor — Why Sex Matters

The Widmark distribution constant 'r' accounts for the proportion of body water — because alcohol distributes only in water, not fat. Males (r = 0.68) have proportionally more body water than females (r = 0.55) due to differences in body composition. This means a 140 lb woman and a 140 lb man drinking the same number of drinks will have meaningfully different BAC levels — the woman's will be higher. Additionally, women typically have lower levels of alcohol dehydrogenase (ADH), the enzyme that begins metabolising alcohol in the stomach before it reaches the bloodstream.

Alcohol Elimination — Why Only Time Works

The liver metabolises alcohol at approximately 0.015% BAC per hour — this is a zero-order kinetic process, meaning the rate does not change with the amount present (unlike most drugs). Nothing accelerates this process — not coffee (masks sedation but doesn't lower BAC), not cold water, not food (slows absorption but doesn't speed elimination), not exercise, not sleep. Only time reduces BAC. To estimate sobriety time: divide current BAC by 0.015. A BAC of 0.12% requires 8 hours to reach 0.00% (0.12 ÷ 0.015 = 8 hours).

US Legal Limits — State by State

49 states + DC: BAC ≥0.08% is illegal for drivers aged 21+ (DUI/DWI per se)
Utah: BAC ≥0.05% is illegal — the strictest standard in the US
Commercial drivers (CDL): BAC ≥0.04% is illegal in all states (federal law)
Under 21 (all states): Zero tolerance — typically ≥0.00–0.02% is illegal depending on state
Aviation: FAA prohibits flying with BAC ≥0.04% or within 8 hours of drinking

NM Dr. Nikhil Mahajan, PT, MPT · Reviewed January 15, 2025 · View credentials

Frequently Asked Questions

Does eating food lower your BAC?

Food does not lower your BAC after alcohol has been absorbed — it only slows absorption rate if consumed before or during drinking. Food in the stomach (particularly high-fat, high-protein foods) slows gastric emptying and delays alcohol from passing into the small intestine where rapid absorption occurs. This means peak BAC is reached later and the peak is lower — but the total alcohol entering your bloodstream is the same. Once alcohol is in your bloodstream, food cannot remove it. Only time and liver metabolism reduce BAC.

Can I fail a breathalyzer below 0.08% BAC?

Yes — you can be arrested for impaired driving at any BAC in most states under "impaired to the slightest degree" laws, even below 0.08%. The 0.08% threshold is the "per se" limit where impairment is legally presumed — but police can charge DUI below this if they observe impaired driving behavior (weaving, failing field sobriety tests). Additionally, Utah's limit is 0.05%, and under-21 zero-tolerance laws mean a BAC as low as 0.01–0.02% can result in a DUI charge for underage drivers.

How accurate is the Widmark BAC formula?

The Widmark Formula provides a population-level statistical estimate — not a precise measurement for any individual. Accuracy is affected by: (1) Individual variation in alcohol metabolism rate (0.010–0.025%/hour in the population, vs the 0.015% average used here); (2) Stomach contents and absorption rate; (3) Medications (certain drugs dramatically slow or speed alcohol metabolism); (4) Liver health (liver disease reduces elimination rate); (5) Genetic variations in alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) enzymes; (6) Tolerance (experienced drinkers may feel less impaired but have the same BAC). The only legally accurate BAC measurement is a blood test or evidentiary breathalyzer administered by law enforcement.

What is alcohol poisoning and when should I call 911?

Alcohol poisoning (severe alcohol intoxication) is a life-threatening emergency typically associated with BAC ≥0.25%. Signs requiring immediate emergency services (call 911): unconsciousness or unresponsiveness (cannot be awakened); slow or irregular breathing (fewer than 8 breaths per minute); blue-tinged or pale skin; hypothermia (cold, clammy skin); seizures; vomiting while unconscious (aspiration risk). Do NOT leave an alcohol-poisoned person alone to "sleep it off" — they can stop breathing or aspirate vomit fatally. Place them in the recovery position (on their side) and stay with them until emergency services arrive. Time is critical — BAC continues rising after the last drink as absorption continues.