BAC Calculator — Blood Alcohol Content

Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.

Formula

BAC = (Alcohol × 5.14 / Weight × r) - (0.015 × hours)

The Widmark formula estimates BAC from alcohol consumed, body weight, sex, and elapsed time. Alcohol volume is in fluid ounces of pure ethanol (one US standard drink is 0.6 fl oz, about 14 g), weight is in pounds, and r is the Widmark distribution factor: 0.68 for men and 0.55 for women. Metabolism removes roughly 0.015 percentage points of BAC per hour. This is an estimate for education only: absorption rate, food, medication and individual physiology move real BAC well away from the calculated figure, and it must never be used to decide whether to drive.

Worked Examples

Example 1: Calculate BAC After Drinks

Problem:180 lb male, 3 beers over 2 hours.

Solution:Using Widmark formula: Weight: 180 lbs Sex factor (r): 0.68 (male) Alcohol: 3 × 0.6 oz = 1.8 oz Time: 2 hours Raw BAC = (1.8 × 5.14) / (180 × 0.68) = 9.25 / 122.4 = 0.076% After metabolism (0.015%/hr × 2hr = 0.03%): BAC = 0.076% - 0.030% = 0.046% Just under legal limit but impaired.

Result:BAC: 0.046% (below 0.08% but impaired)

Example 2: Time to Sober Calculation

Problem:Current BAC is 0.12%. How long until sober?

Solution:Current BAC: 0.12% Metabolism rate: 0.015%/hour Time to reach 0.08%: (0.12 - 0.08) / 0.015 = 2.7 hours Time to reach 0.00%: 0.12 / 0.015 = 8 hours DO NOT DRIVE for at least 8 hours. Even after 3 hours (at 0.075%), you're impaired.

Result:8 hours to sober, 2.7 hours to legal limit

Example 3: Compare Male vs Female

Problem:Same weight (150 lbs), same drinks (2 glasses wine). Compare BAC.

Solution:Alcohol: 2 × 0.6 oz = 1.2 oz Weight: 150 lbs Male (r = 0.68): BAC = (1.2 × 5.14) / (150 × 0.68) = 6.17 / 102 = 0.060% Female (r = 0.55): BAC = (1.2 × 5.14) / (150 × 0.55) = 6.17 / 82.5 = 0.075% Female BAC is about 24% higher from the same alcohol, because 0.68 / 0.55 = 1.24.

Result:Male: 0.060% vs Female: 0.075%

Frequently Asked Questions

What is BAC?

Blood Alcohol Concentration (BAC) is the percentage of alcohol in your bloodstream. 0.08% means 0.08 grams of alcohol per 100 mL of blood. 0.08% is the per se driving limit in most US states, but Utah sets 0.05%, much of Europe and Australia use 0.05%, and some countries are lower still. Impairment starts well below any of these limits.

How accurate are BAC calculators?

BAC calculators provide estimates only. Actual BAC depends on many factors: food in stomach, drinking speed, individual metabolism, medications, liver health, and genetics. Use calculators for general awareness, not to decide if you're safe to drive.

What is a standard drink?

One standard drink contains about 0.6 oz (14g) of pure alcohol: 12 oz beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%). Craft beers, large pours, and strong cocktails often contain more than one standard drink.

How does body weight affect BAC?

Heavier people have more body water to dilute alcohol, resulting in lower BAC from the same amount of alcohol. However, this doesn't mean heavier people are 'safer' drivers - impairment still occurs at the same BAC levels regardless of weight.

Why do women reach higher BAC than men?

Women typically have: less body water (alcohol dilutes more in water), more body fat (doesn't absorb alcohol), lower levels of alcohol dehydrogenase enzyme, and hormonal variations affecting metabolism. Same drinks result in higher BAC for women.

Does eating food help?

Eating before or while drinking slows alcohol absorption, reducing peak BAC. However, the total alcohol is still absorbed - it just takes longer. Food doesn't make you 'less drunk' in the end, just delays the peak. Never rely on food to drive safely.

How fast does the body process alcohol?

The liver metabolizes alcohol at about 0.015% BAC per hour (roughly one standard drink). This rate is mostly constant - coffee, cold showers, and exercise don't speed it up. Time is the only cure for intoxication.

What happens at different BAC levels?

0.02-0.03%: Mild relaxation. 0.05-0.06%: Lowered inhibitions, impaired judgment. 0.08%: Per se limit in most US states, significant impairment. 0.10-0.12%: Poor coordination, slurred speech. 0.15%+: Serious impairment. 0.30%+: Risk of blackout, coma, death.

Can I sober up quickly?

No. Only time reduces BAC. Coffee may make you feel more alert but doesn't reduce impairment. Exercise, cold showers, and other 'tricks' don't work. Your liver processes alcohol at a fixed rate that can't be accelerated.

Is 0.08% really impaired?

Yes. At 0.08%, you have: significantly impaired reaction time, reduced coordination, difficulty steering, impaired judgment about speed and distance. NHTSA reports that crash risk rises steeply across this range rather than jumping at one threshold. Many jurisdictions set lower limits: Utah and much of Europe use 0.05%, and Japan uses 0.03%.

Background & Theory

Blood Alcohol Concentration (BAC) measures alcohol in your bloodstream. The Widmark formula estimates BAC based on drinks consumed, body weight, sex, and time.

Widmark Formula:
BAC = (Alcohol oz × 5.14 / Weight × r) - (0.015 × hours)

Where r = 0.68 for males, 0.55 for females

Standard Drinks:

12 oz beer (5%) = 0.6 oz alcohol
5 oz wine (12%) = 0.6 oz alcohol
1.5 oz spirits (40%) = 0.6 oz alcohol

BAC Impairment Levels:

BAC	Effects
0.02%	Slight relaxation, warmth
0.05%	Lowered alertness, impaired judgment
0.08%	Per se limit in most US states; poor coordination
0.10%	Slurred speech, slow reactions
0.15%	Difficulty walking, vomiting
0.20%	Confusion, blackout risk
0.30%+	Risk of coma, death

Metabolism:

Liver processes ~0.015% BAC per hour
Rate is mostly constant
Cannot be accelerated

Factors Affecting BAC:

Body weight
Sex
Food in stomach
Drinking speed
Alcohol tolerance
Medications
Liver health

Legal Limits Vary:
0.08% is the per se limit in most US states, but Utah uses 0.05%. Much of Europe and Australia use 0.05%, Japan uses 0.03%, and several countries set 0.02% or zero. Commercial drivers and drivers under 21 face much lower limits almost everywhere. Always check the limit where you are driving.

Safe Driving:
The only safe BAC for driving is 0.00%. Impairment begins below every legal limit.

History

Blood alcohol measurement began in the early 20th century as automobiles became common and drunk driving emerged as a public safety issue. Swedish scientist Erik Widmark developed the foundational formula in the 1920s-30s, creating a mathematical model relating alcohol consumption to blood concentration. The first drunk driving laws appeared in the US in the 1910s, but lacked objective BAC standards. Officers relied on subjective assessment of intoxication. The breathalyzer, invented by Robert Borkenstein in 1954, provided a practical field testing method. Early legal limits varied widely. Through the 1960s-70s, limits of 0.10-0.15% were common in the US. Research increasingly showed that significant impairment occurs at lower levels, leading to gradual tightening of standards. The 0.08% limit was first adopted by Utah in 1983. Federal highway funding incentives (starting 2000) pushed all states to adopt 0.08% by 2004. Many countries use lower limits: 0.05% in most of Europe and Australia, 0.03% in Japan, and 0.00% in some countries. Modern understanding emphasizes that impairment begins at the first drink. Even at 0.02% BAC, driving ability is affected. The trend continues toward lower limits - Utah became the first state to adopt 0.05% in 2018. Advocacy groups push for wider adoption of 0.05% standards.