Blood Alcohol Level Calculator (BAC Estimator)

Estimate blood alcohol content from drinks, weight, and time using the Widmark equation. Educational only — never use to decide if it's safe to drive.

July 4, 2026

Educational estimate only — never use this to decide whether it's safe to drive.

Actual blood alcohol content depends on individual metabolism, food intake, medications, and many other factors this formula cannot capture. If you've been drinking at all, the only safe choice is zero tolerance — use a rideshare, a taxi, or a sober driver instead of estimating your own BAC to judge driving fitness.

Sex (affects distribution ratio)

Body Weight

How do you want to enter drinks?

Standard Drinks (14 g pure alcohol each)

1 standard drink ≈ 12 oz beer (5% ABV), 5 oz wine (12% ABV), or 1.5 oz spirits (40% ABV) — NIAAA definition.

Hours Since First Drink

Estimated BAC

0.035%

Low estimated level

Total alcohol consumed ≈ 28.0 g. Reference only — the US per se legal driving limit is 0.08% in most states, shown here for educational context, not as a driving-safety threshold.

Remember: this number is an estimate, not a measurement. Never use it to decide whether it's safe to drive — call a rideshare or a sober driver instead.

Uses the Widmark equation: BAC(%) = [(grams of alcohol × 100) ÷ (body weight in grams × distribution ratio r)] − (elimination rate β × hours elapsed). Default r = 0.68 (male) / 0.55 (female) — the most common consumer-calculator convention; more conservative alternates of 0.73/0.66 also appear in the literature. β is fixed at 0.015%/hour (NIAAA-aligned average), though individual elimination rates range roughly 0.010–0.030%/hour depending on metabolism, liver function, tolerance, and food intake. This estimate does not account for absorption delay, food, medications, or other individual factors, and can be meaningfully wrong for any single person. It is an educational tool only — not a medical, legal, or driving-safety determination.

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Reference Values

Last verified: Jul 4, 2026

Category	Range	What It Means	Status
Standard drink (US, NIAAA)	14 g pure alcohol	Defined as 12 oz regular beer (~5% ABV), 5 oz table wine (~12% ABV), or 1.5 oz distilled spirits (~40% ABV / 80-proof) — all contain roughly the same 14 g of pure ethanol.	Good
Male distribution ratio (r)	≈0.68	Most common consumer-calculator convention for the Widmark factor in men. A more conservative alternate value of 0.73 is sometimes used in forensic contexts.	Good
Female distribution ratio (r)	≈0.55	Most common consumer-calculator convention for the Widmark factor in women, reflecting typically higher body-fat percentage and lower body-water content. A more conservative alternate value of 0.66 is sometimes used.	Good
Alcohol elimination rate (β)	0.015 %/hour	NIAAA-aligned average metabolism rate used as the standard constant. Individual literature range is 0.010–0.030 %/hour depending on liver function, tolerance, food intake, and other factors.	Okay
US per se legal driving limit	0.08% BAC	Federal/most-states threshold for driving under the influence — shown for reference only. This calculator is not a fitness-to-drive tool and this value should never be used to decide whether it's safe to drive.	Poor
Commercial driver (CDL) limit	0.04% BAC	Lower federal threshold for commercial vehicle operators — shown for reference only.	Poor
Zero-tolerance / underage limit	0.00–0.02% BAC	Most US states apply a near-zero limit for drivers under 21 — shown for reference only.	Poor

Source: Widmark equation constants and standard drink definition per the National Institute on Alcohol Abuse and Alcoholism (NIAAA, niaaa.nih.gov). Legal BAC limits per NHTSA/state DMV publications, included for educational context only — not driving-safety guidance.

Worked Examples

180 lb Male, 2 Standard Drinks, 1 Hour

Sex: Male
Weight: 180 lb
Drinks: 2 standard drinks (28 g alcohol)
Hours elapsed: 1

≈0.035% BAC

28 g ÷ (81,646.6 g body weight × 0.68) × 100 = 0.0504% raw, minus (0.015 × 1) = ≈0.035%.

140 lb Female, 3 Glasses of Wine, 2 Hours

Sex: Female
Weight: 140 lb
Drinks: 3 standard drinks (42 g alcohol)
Hours elapsed: 2

≈0.090% BAC

42 g ÷ (63,502.9 g body weight × 0.55) × 100 = 0.1203% raw, minus (0.015 × 2 = 0.03) = ≈0.090%.

200 lb Male, 4 Beers (12 oz, 5% ABV), 3 Hours

Sex: Male
Weight: 200 lb
Drinks: 4 beers (12 oz, 5% ABV ≈ 14 g each = 56 g)
Hours elapsed: 3

≈0.046% BAC

56 g ÷ (90,718.4 g body weight × 0.68) × 100 = 0.0908% raw, minus (0.015 × 3 = 0.045) = ≈0.046%.

70 kg Female, 1 Shot of Spirits (1.5 oz, 40% ABV), 0.5 Hours

Sex: Female
Weight: 70 kg
Drinks: 1 shot (1.5 oz, 40% ABV ≈ 14 g)
Hours elapsed: 0.5

≈0.029% BAC

14 g ÷ (70,000 g body weight × 0.55) × 100 = 0.0364% raw, minus (0.015 × 0.5 = 0.0075) = ≈0.029%.

160 lb Male, 6 Drinks Over 5 Hours (Long Session)

Sex: Male
Weight: 160 lb
Drinks: 6 standard drinks (84 g alcohol)
Hours elapsed: 5

≈0.095% BAC

84 g ÷ (72,574.7 g body weight × 0.68) × 100 = 0.1702% raw, minus (0.015 × 5 = 0.075) = ≈0.095%, showing that even spread over 5 hours, 6 drinks can leave BAC well above the 0.08% reference point — pacing and total volume both matter.

How to Use This Calculator

1

Enter your sex and body weight

These set the distribution ratio (r) and total body water used in the Widmark formula. Switch between lb and kg as needed.
2

Enter your drinks

Either type in a number of standard US drinks (14 g alcohol each), or switch to the drink builder to enter volume and ABV% for beer, wine, spirits, or a custom drink.
3

Enter hours since your first drink

The calculator subtracts the estimated amount your body has already metabolized during that time.
4

Read your estimated BAC — and the disclaimer

The result shows an estimated percentage plus a permanent reminder that this is an educational estimate, not a driving-safety or legal determination.

What Each Value Means

Estimated BAC (% BAC): Blood alcohol content expressed as a percentage (grams of alcohol per 100 mL of blood), estimated using the Widmark equation from drinks consumed, body weight, sex, and time elapsed.
Distribution ratio (r) (ratio): A population-average constant approximating how alcohol distributes through body water — higher in men, lower in women, on average — used to convert total alcohol grams into a concentration estimate.
Elimination rate (β) (%/hour): The average rate at which the body metabolizes and clears alcohol from the bloodstream over time, commonly modeled at about 0.015% per hour.

Frequently Asked Questions

Can I use this calculator to decide if I'm safe to drive?

No. This calculator produces a rough educational estimate based on average population constants — it is not a breathalyzer, not a legal determination, and not a fitness-to-drive test. Actual BAC depends on factors this formula can't measure, like your exact metabolism, stomach contents, medications, and hydration. If you've had any alcohol, the only safe choice is to not drive — use a rideshare, taxi, or sober driver instead.

What is the Widmark equation?

The Widmark equation is the standard formula used to estimate blood alcohol content from the amount of alcohol consumed, body weight, sex, and time elapsed. Developed by Swedish physiologist Erik Widmark in the 1930s, it remains the basis for most consumer and forensic BAC estimates today, expressed as BAC(%) = [(grams of alcohol × 100) ÷ (body weight in grams × distribution ratio r)] − (elimination rate × hours elapsed).

Why does the calculator ask for sex, and why are the numbers different?

The formula uses a 'distribution ratio' (r) that approximates how alcohol spreads through body water. Men have, on average, a higher proportion of body water and lower body fat than women of the same weight, so alcohol is diluted more per pound — this calculator uses r ≈ 0.68 for men and r ≈ 0.55 for women, the most common consumer-calculator convention. These are population averages, not individual measurements, so any one person's actual ratio can differ.

How accurate is a BAC estimate like this?

Not very, in an absolute sense — and that's an important limitation, not a footnote. Published research shows individual BAC can vary substantially from the Widmark estimate due to food in the stomach (which slows absorption), medications, hydration, body composition, and genetic differences in alcohol metabolism enzymes. Treat the result as a rough educational figure, not a precise measurement — only a breathalyzer or blood test gives an actual reading.

Why does my estimated BAC go down over time in the calculator?

The body eliminates alcohol at a roughly steady rate once absorption is complete, commonly modeled at about 0.015% per hour on average. The calculator subtracts this elimination amount based on the hours you enter since your first drink. This rate varies person to person (roughly 0.010–0.030%/hour in the research literature), which is another reason the result is an estimate rather than an exact figure.