BAC Calculator - Blood Alcohol Content Estimator

How to use this tool

Add your drinks. Select drink types from presets or enter custom volumes and ABV.
Enter your details. Provide your weight, biological sex, and how long you have been drinking.
View your BAC estimate. See your estimated BAC, impairment category, time until sober, and estimated time to the selected legal threshold.

How the Widmark BAC formula works

The Widmark formula is the internationally recognized method for estimating blood alcohol content. It relates the amount of alcohol consumed to body weight, sex, and time:

BAC = (A / (W × r × 10)) − (0.015 × H)

Where A = grams of pure alcohol, W = body weight in kg, r = Widmark factor (0.73 for males, 0.66 for females reflecting body water percentage), and H = hours since drinking began. The result is multiplied to express BAC as a percentage (g/dL).

BAC and impairment

Even at low BAC levels, alcohol affects judgment, reaction time, and coordination. The US federal legal driving limit of 0.08% is not a "safe" threshold; impairment begins measurably at 0.02–0.05%. Commercial drivers are held to a 0.04% limit; zero-tolerance laws apply to drivers under 21 in all US states.

Factors that affect BAC

Body weight: heavier individuals have more body water to dilute alcohol.
Sex: females generally have a lower body water percentage (Widmark r).
Food: eating slows absorption, lowering the peak BAC.
Drinking rate: the liver eliminates ≈1 standard drink per hour; faster drinking exceeds this.
Medications & health: many medications interact with alcohol and amplify impairment.

Important disclaimer

BAC level effects reference

The following scale describes the typical behavioral effects at each BAC range. Individual responses vary significantly.

BAC (%)	Typical effects	Legal status (US)
0.02–0.03	Mild relaxation, slight mood elevation, minor impairment of judgment and visual tracking	Legal to drive; zero-tolerance applies under 21
0.04–0.06	Lowered inhibitions, reduced concentration, impaired minor motor skills	Legal to drive for most adults; commercial drivers over limit
0.07–0.09	Clearly impaired reaction time and coordination; slightly slurred speech; overconfidence	At or near legal DUI limit (0.08% in US)
0.10–0.12	Significant motor impairment; slurred speech; difficulty with complex tasks	Legally impaired - DUI
0.13–0.15	Severe coordination loss; seriously impaired balance and reaction time; dysphoria may appear	DUI
0.16–0.19	Nausea, disorientation, loss of balance	DUI - high-BAC enhancement in many states
0.20–0.24	Confusion, stupor, blackout risk; needs assistance to walk	DUI / alcohol poisoning risk
0.25–0.29	Severe impairment; risk of unconsciousness; aspiration danger	Medical emergency territory
0.30+	Loss of consciousness; coma; life-threatening suppression of respiratory and cardiac function	Potential fatality

Legal BAC limits worldwide

Country / Region	General limit	Notes
United States	0.08%	Commercial drivers: 0.04%; under 21: 0.00–0.02% depending on state
Canada	0.08%	Administrative suspension at 0.05% in most provinces
United Kingdom (England/Wales)	0.08%	Scotland: 0.05%
Germany	0.05%	Zero tolerance for new drivers (<21) and commercial drivers
France	0.05%	New drivers (≤3 years): 0.02%
Australia	0.05%	0.00% for learner/provisional drivers and commercial drivers
Japan	0.03%	Strict enforcement; passengers can also be penalized
Sweden / Norway	0.02%	Among the strictest in Europe
Russia / Czech Republic	0.00%	Absolute zero-tolerance

Time to sober up

The liver metabolizes alcohol at a nearly constant rate - approximately 0.015% BAC per hour (one standard drink per hour for a typical adult). This rate is largely fixed by biology; it does not speed up meaningfully with common folk remedies:

Coffee: caffeine makes you feel more alert but does not reduce BAC or improve driving ability. It produces a "wide-awake drunk" effect.
Food: eating slows absorption and lowers peak BAC, but has little effect on elimination once alcohol is already in your bloodstream.
Sleep: your liver continues metabolizing while you sleep, but sleep itself does not accelerate the process.
Exercise or cold shower: no scientific evidence supports faster metabolism from either.

Example: a person who reaches 0.12% BAC needs approximately (0.12 − 0.00) ÷ 0.015 = 8 hours to reach 0.00%, assuming no further drinks. Plan accordingly before driving the morning after a night out.

Frequently asked questions

How is BAC calculated?

This calculator uses the Widmark formula: BAC = (grams of alcohol ÷ (body weight in kg × distribution ratio × 10)) − (0.015 × hours drinking). The distribution ratio (r) is 0.73 for males and 0.66 for females, reflecting differences in body water percentage.

How accurate is this BAC estimate?

The Widmark formula provides a general estimate. Actual BAC varies based on individual metabolism, liver function, food intake, medications, hydration, and drinking rate. Use this tool for educational purposes only - do not use it to make decisions about driving or operating machinery.

Does eating reduce BAC?

Food does not reduce BAC - it cannot speed up alcohol metabolism. However, eating before or during drinking slows the absorption of alcohol, meaning your BAC rises more slowly and peaks at a lower level. This calculator does not account for food, so actual BAC may be somewhat lower if you ate.

Can I speed up sobering up?

No. Coffee, cold showers, exercise, and food do not speed up alcohol elimination. Only time allows the liver to metabolize alcohol - at roughly 0.015% BAC per hour on average. This rate is relatively fixed and varies little between individuals.

What is the legal driving limit?

In the United States, the general limit is 0.08% BAC for drivers 21 and older. Utah uses 0.05%, commercial drivers have a 0.04% limit, and under-21 laws vary; this calculator uses 0.00% as a conservative under-21 threshold. Legal limits vary by jurisdiction and are not safe-to-drive guarantees. Never use an estimate to decide whether to drive.