BAC Calculator — Free Blood Alcohol Content Calculator 2026

How Accurate Is a BAC Calculator?

A BAC calculator is a reliable educational estimate — not a certified breathalyzer reading. The most accurate BAC calculators use the Widmark formula, which is the same mathematical basis used by forensic toxicologists and law enforcement agencies worldwide.

Our BAC calculator is built on the Widmark formula with the following accuracy factors built in:

• Biological sex — Women have a lower volume of distribution (r = 0.55) compared to men (r = 0.68), meaning alcohol concentrates more rapidly in female body tissue at the same weight and drink count
• Body weight — Heavier individuals have more body water, which dilutes alcohol more effectively
• Stomach content — Food in the stomach slows alcohol absorption significantly. An empty stomach absorbs alcohol up to 3x faster than a full stomach
• Drink strength (ABV%) — Our calculator accepts custom ABV percentages for non-standard drinks rather than assuming a fixed alcohol content
• Hours drinking — The liver metabolises approximately 0.015% BAC per hour regardless of sex, weight, or food intake

Even the most accurate BAC calculator available cannot account for individual variation in liver enzyme activity, medication interactions, or fatigue. Use the result as a guide, not a guarantee.

BAC by Weight — How Body Weight Affects Alcohol

Body weight is one of the two most important variables in any BAC calculation. The relationship is direct and linear — the more you weigh, the more body water you have, and the more diluted your blood alcohol becomes after the same number of drinks.

Here is a practical comparison for a male drinking 3 standard beers (12oz, 5% ABV) over 2 hours with a light meal:

• 140 lbs: Estimated BAC ~0.072% — approaching the legal limit
• 160 lbs: Estimated BAC ~0.061% — below the limit but impaired
• 200 lbs: Estimated BAC ~0.046% — below the limit
• 240 lbs: Estimated BAC ~0.036% — well below the limit

The same 3 drinks put a 140 lb person near the legal threshold while leaving a 240 lb person at half that level. This is why BAC by weight calculations matter — there is no universal “number of drinks” that is safe for everyone.

BAC calculator for women vs men — at the same weight, a woman will typically reach a BAC 15–20% higher than a man after the same number of drinks. This is due to the lower water-to-body-mass ratio and lower average alcohol dehydrogenase enzyme activity in women. Our calculator adjusts the Widmark r-factor automatically when you select Female.

How Food and Stomach Content Affect BAC

The stomach content input in our BAC calculator — Empty, Light, or Full — has a larger impact on your result than most people expect.

Empty stomach: Alcohol enters the bloodstream within 30 minutes. Peak BAC is reached quickly and is significantly higher than the same drinks consumed with food. If you have not eaten in 4+ hours, select Empty.

Light meal: A snack or light meal slows gastric emptying moderately. Alcohol absorption takes 45–90 minutes to peak. This is the most common real-world scenario for social drinking.

Full meal: A large meal with protein and fat slows alcohol absorption dramatically. Peak BAC may not be reached for 1–2 hours, and the peak itself is 20–35% lower than on an empty stomach. The same number of drinks that push you over the legal limit on an empty stomach may keep you under it after a full meal — though impairment still occurs.

One thing food does not do is reduce your total BAC over a full evening. It only delays and reduces the peak. Your liver still processes approximately 0.015% BAC per hour regardless of what you ate.

How Long Until BAC Reaches Zero?

The “time to zero BAC calculator” function is one of the most searched features — and one of the most misunderstood.

Your liver eliminates alcohol at a fixed rate of approximately 0.015% BAC per hour. This rate does not change based on coffee, water, exercise, cold showers, or any other folk remedy. The only variable is time.

To estimate when your BAC reaches zero:

Hours to sober = Current BAC ÷ 0.015

Examples:

• BAC 0.08% → approximately 5.3 hours to reach zero
• BAC 0.15% → approximately 10 hours to reach zero
• BAC 0.20% → approximately 13.3 hours to reach zero

This is why a heavy night of drinking can leave measurable BAC the following morning — a BAC of 0.15% reached at midnight means you are not at zero until approximately 10am the next day.

Our BAC calculator over time function accounts for this elimination rate automatically based on your hours drinking input. If you are trying to calculate BAC since last drink, enter the hours elapsed since you stopped drinking.

If your estimated BAC is significantly above 0.08% and you are wondering about the legal and financial consequences of a DUI charge, our DUI Calculator can estimate the full cost — fines, attorney fees, SR-22 insurance, and ignition interlock device expenses — broken down by state and offense number.

The Widmark Formula — How BAC Is Calculated

Our BAC calculator formula is based on the Widmark equation, developed by Swedish physician Erik Widmark in the 1930s and still used today in forensic toxicology and DUI prosecution.

The Widmark Formula:

BAC = (Alcohol consumed in grams) ÷ (Body weight in grams × r) − (0.015 × hours)

Where:

• Alcohol in grams = Volume of drink (oz) × ABV% × 0.789 (density of ethanol) × 29.57 (ml per oz)
• r = Widmark factor — 0.68 for males, 0.55 for females
• 0.015 = Average hourly elimination rate

Example calculation: A 160 lb (72.6 kg) male drinks 2 standard beers (12oz, 5% ABV) over 1 hour with a light meal.

Alcohol in grams = 2 × 12 × 0.05 × 0.789 × 29.57 = 28.1g BAC before elimination = 28.1 ÷ (72,600 × 0.68) = 0.0569% Minus elimination = 0.0569 − (0.015 × 1) = ~0.042% BAC

The food modifier in our calculator applies an absorption reduction factor of approximately 10–30% depending on meal size, which reflects the gastric emptying delay documented in clinical studies.

How to calculate BAC level accurately — the formula above gives you the mathematical basis. Our calculator handles this automatically including the food modifier and custom ABV input, which most basic BAC calculators do not support.

If law enforcement uses a breathalyzer or blood test to establish BAC at the time of a DUI stop, they may use retrograde extrapolation — working backwards from a later test to estimate BAC at the time of driving. Understanding how BAC is calculated and eliminated can be critical in a DUI defense. For an estimate of what a DUI charge could cost you financially, see our DUI Cost Estimator — it covers attorney fees, state-specific fines, SR-22 surcharges, and more.

BAC Levels and Legal Limits by Country

Our BAC calculator supports multiple countries with their specific legal limits built in. Here is a reference for the most commonly searched limits:

United States — 0.08% BAC The legal limit for drivers over 21 is 0.08% in all 50 states. Commercial drivers face a lower limit of 0.04%. For drivers under 21, zero tolerance laws apply in most states — any detectable BAC (0.01–0.02%) can result in a DUI charge. High BAC thresholds for aggravated DUI charges are typically 0.15–0.16% depending on state.

United Kingdom — 0.08% in England/Wales, 0.05% in Scotland Scotland lowered its legal limit from 0.08% to 0.05% in 2014, aligning with most of Europe. England and Wales retain the 0.08% limit.

Canada — 0.08% (criminal), 0.05% (administrative) Canada has a two-tier system. A BAC of 0.05–0.079% triggers administrative penalties including license suspension. A BAC of 0.08%+ is a criminal offence under the Criminal Code.

Australia — 0.05% Australia’s national limit is 0.05% for fully licensed drivers. Learner and provisional drivers face zero tolerance (0.00%) across all states.

European Union — 0.05% (most countries) Most EU countries operate at 0.05%, with some including Hungary, Czech Republic, and Slovakia at 0.00% for all drivers.

0.00% — Zero Tolerance Countries Several countries including Hungary, Slovakia, Czech Republic, and Saudi Arabia maintain a zero tolerance policy — any detectable alcohol is illegal while driving.

Frequently Asked Questions

How accurate is a BAC calculator? A BAC calculator using the Widmark formula is accurate within approximately ±15–20% for most people under typical conditions. Individual factors that affect accuracy include liver enzyme variation, medication interactions, carbonation of drinks (speeds absorption), and altitude. For a precise reading, only a certified breathalyzer or blood test can confirm your actual BAC.

How do you calculate BAC by weight? BAC by weight uses the Widmark formula: divide the grams of alcohol consumed by your body weight in grams multiplied by the Widmark r-factor (0.68 for males, 0.55 for females), then subtract 0.015 multiplied by the hours elapsed. Our calculator handles this automatically — just enter your weight in lbs or kg.

How long does it take for BAC to reach zero? The liver eliminates approximately 0.015% BAC per hour. At a BAC of 0.08%, it takes roughly 5.3 hours to reach zero. At 0.15%, approximately 10 hours. Nothing — coffee, water, food, or exercise — speeds up this process. Only time reduces BAC.

Is a BAC calculator for women different from men? Yes. The female Widmark r-factor is 0.55 compared to 0.68 for males, which means at the same body weight, women reach a higher BAC from the same drinks. Our calculator adjusts this automatically when you select Female under Biological Sex.

What BAC level is illegal to drive? In the United States, 0.08% is the legal limit for drivers 21 and over. In Australia and most of Europe, the limit is 0.05%. In zero tolerance countries including Hungary and Czech Republic, any detectable BAC is illegal. Our calculator displays your estimated BAC alongside the legal limit for your selected country.

Can I use a BAC calculator to decide if I am safe to drive? No. Impairment begins well below the legal limit — reaction times and judgment are affected at BAC levels as low as 0.02%. A BAC calculator gives an estimate, not a certified reading, and cannot account for individual variation. If you have been drinking, the safest decision is always not to drive. If you have already been charged with a DUI, our DUI Calculator can help you understand the financial consequences by state.

What is the Widmark formula? The Widmark formula is BAC = (grams of alcohol ÷ (body weight in grams × r)) − (0.015 × hours). It was developed by Swedish physician Erik Widmark in the 1930s and remains the standard method for forensic BAC calculation used in DUI prosecution and toxicology worldwide.

Does food lower your BAC? Food does not lower BAC — it delays and reduces the peak. Eating before or during drinking slows alcohol absorption by up to 35%, which means your BAC rises more slowly and peaks lower. However, your total BAC over the evening is the same, and your elimination rate of 0.015% per hour is unchanged.

Data Source

BAC estimates in this calculator use the Widmark formula — the forensic standard for blood alcohol content estimation, developed by Swedish physician
Erik Widmark in 1932 and validated in peer-reviewed pharmacokinetic research:

BAC = (Alcohol consumed in grams) ÷ (Body weight in grams × Distribution factor) − (Elimination rate × Hours elapsed)

Distribution factors (r): 0.68 for males, 0.55 for females — sourced from Widmark (1932) and confirmed in Taylor et al., “Determination of Blood Alcohol in
a National Sample” (Journal of Studies on Alcohol, 2009).

Alcohol elimination rate: 0.015% BAC per hour — the average published in National Highway Traffic Safety Administration (NHTSA) Technical Report DOT HS 811 336, and used by law enforcement and forensic toxicologists for retrograde extrapolation.

Standard drink definitions sourced from:
→ US: NIAAA (National Institute on Alcohol Abuse and Alcoholism) — 14g pure alcohol = 1 standard drink
→ UK: NHS — 8g pure alcohol = 1 unit
→ Australia: Australian Government NHMRC — 10g = 1 std
→ Canada: Canadian Centre on Substance Use — 13.6g = 1 std

Legal BAC limits sourced from:
→ US: NHTSA state-by-state DUI limit database (2026) Most states: 0.08% / Utah: 0.05%
→ UK: DVLA — 0.08% England/Wales/NI; 0.05% Scotland
→ Australia: ATC — 0.05% national (0.00% for learners)
→ Canada: Transport Canada — 0.08% criminal; 0.05% provincial administrative

CRITICAL DISCLAIMER: This calculator provides estimates for educational purposes only. Individual BAC is affected by food intake, medication, fatigue,
hydration, liver function, and genetic factors that this formula cannot account for. Never use this calculator to determine fitness to drive. A certified
breathalyser or blood test is the only reliable measure of actual BAC.

Related Calculators

• DUI Calculator — If your BAC was at or above the legal limit and you were stopped, understand the full financial cost of a DUI charge. Covers fines, SR-22 insurance, attorney fees, and ignition interlock costs by state.
• Personal Injury Calculator — If a DUI-related accident resulted in injury, estimate potential settlement and liability costs.