BAC Calculator (Blood Alcohol Content)

Estimate blood alcohol content based on drinks consumed, body weight, and time. For educational purposes only.

By Konstantin Iakovlev · Updated September 2026 · Source: NHTSA — Drunk Driving

Disclaimer: This calculator is for educational purposes only. Actual BAC varies based on many factors. Never drink and drive regardless of estimated BAC.
Sex
lbs
hrs

Estimated BAC

0.040%

Some Impairment

Legal Status

Under Limit

0.08% limit (0.05% in Utah)

Time Until Sober

2.7 hrs

Details

Total Alcohol Consumed42.0 g
Estimated BAC0.0405%
Metabolism Rate0.015%/hr
Est. Time to 0.00%2.7 hours

BAC Impairment Levels

Sober0.00%
Minimal Impairment0.01-0.03%
Some Impairment0.04-0.07%
Legally Impaired0.08-0.14%
Severely Impaired0.15%+

The 0.08% per se limit shown here applies in 49 states and the District of Columbia. Utah has been 0.05% since December 30, 2018, and it applies to out-of-state drivers too, so a reading this tool calls “under limit” can still be over the limit in Utah. Lower thresholds also apply to drivers under 21 (zero-tolerance laws) and to commercial drivers (0.04%). This is an estimate from average metabolism — never treat it as evidence that you are safe or legal to drive.

Use the BAC Calculator (Blood Alcohol Content) above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and is not medical advice. Results are estimates from standard formulas and the numbers you enter. Talk to a doctor or another qualified health professional about your own health before acting on them.

How It Works

Blood Alcohol Content is an estimate of the concentration of alcohol in your bloodstream, derived here from how many drinks you have had and what kind, your sex and body weight, and how much time has passed since your first drink. Having even a rough sense of where you stand can support more responsible choices about driving and personal safety. The figures shown are for educational awareness of how alcohol affects the body, nothing more.

The math behind the estimate is a modified version of the Widmark formula, one of the longest-standing methods for approximating BAC. It weighs the grams of alcohol consumed against body weight in kilograms and a gender-specific distribution constant (r), then deducts the alcohol your body eliminates as time passes. The result is a reasonable approximation, though your own metabolism and other physiological traits can push the real number higher or lower.

Treat every reading as a ballpark, never a verdict. Food in your stomach, medications, how hydrated you are, and the particular way your body processes alcohol all shift actual BAC in ways no formula can capture. Do not use these numbers to decide whether you are safe to drive or to do anything else that demands full mental and physical sharpness.

Example: Three Beers Over Two Hours

  1. 1 Sarah weighs 140 lbs and drinks three 12-oz beers at 5% ABV between 8:00 PM and 10:00 PM. The calculator counts each beer as 12 × 29.5735 ml × 5% × 0.789 g/ml = 14.0 grams of alcohol, the size of one U.S. standard drink.
  2. 2 Inputs: Female, 140 lbs, 3 drinks, Beer, 2 hours since the first drink. Alcohol: 3 × 14.0 = 42.0 g. Body weight: 140 × 453.592 = 63,503 g, and with the female distribution constant r = 0.66 that is 41,912 g.
  3. 3 Peak estimate: 42.0 ÷ 41,912 × 100 = 0.100%. Two hours of elimination at 0.015 per hour removes 0.030, so the calculator shows 0.070% (Some Impairment) and about 4.7 hours until it reaches zero.
  4. 4 0.070% is under the 0.08% limit that applies everywhere except Utah, but over Utah's 0.05%. NHTSA already lists impaired judgment and reduced coordination at 0.05%, so she should not drive. Arranging a ride before the first drink is the safe plan.

Source: NHTSA — Drunk Driving · Last updated: September 2026

Frequently Asked Questions

How many drinks does it take to reach 0.08 BAC?
For a 160-lb person, roughly 3-4 standard drinks in one hour may reach 0.08 BAC. A standard drink is 12 oz beer (5% ABV), 5 oz wine (12% ABV), or 1.5 oz liquor (40% ABV). Weight, sex, food intake, and metabolism all affect BAC.
How long does it take for alcohol to leave your system?
The calculator assumes the body clears alcohol at a steady 0.015 BAC per hour. In this model one standard drink raises the BAC of a 160-lb man by about 0.026, so a single drink takes about 1.8 hours to clear. After reaching 0.08 BAC, it takes approximately 5-6 hours to return to zero.
What is the legal BAC limit in the US?
The legal limit for driving is 0.08 BAC in every state, the District of Columbia and Puerto Rico except Utah, which uses 0.05. Commercial drivers may not perform safety-sensitive duties at 0.04 or higher (49 CFR 382.201). For drivers under 21, federal highway funding rules (23 U.S.C. 161) require states to treat a BAC of 0.02 or more as driving under the influence.

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