Blood Alcohol Content (BAC) Calculator
Estimate your blood alcohol content from drinks, body weight, gender, and time elapsed using the forensic-grade Widmark formula. Check legal driving limits for 20+ countries and see exactly how long until you are safely below the limit. Educational and safety tool only — never drive after drinking.
Safety Notice — Read First
This calculator is an educational estimate only. Real blood alcohol content varies based on metabolism, food intake, medications, hydration, body composition, and dozens of other factors. It is not a substitute for a calibrated breathalyzer or blood test.
Never drive if you have been drinking. If in doubt, call a ride, ride a bus, or stay where you are. The cost of a taxi is always less than a DUI — or a life.
Personal Info
The Widmark r constant approximates the proportion of body water that distributes alcohol.
Eating slows alcohol absorption by 10-20%, lowering peak BAC.
Current limit: 8.00% — 0.08% all states. Commercial 0.04%. Under-21 zero tolerance (typically 0.00-0.02%).
Drinks Consumed
Add your drinks and details
Then hit Calculate BAC to see your estimate
Legal Driving Limits Around the World
Blood alcohol driving limits vary dramatically across countries — from zero tolerance in Saudi Arabia, the UAE, and Brazil to 0.08% in the United States and parts of the UK. Always check the local limit before driving abroad.
| Country / Region | General Limit | Notes |
|---|---|---|
| United States | 8.00% | 0.08% all states. Commercial 0.04%. Under-21 zero tolerance (typically 0.00-0.02%). |
| United Kingdom (Eng/Wales/NI) | 8.00% | 80 mg/100 ml. Often expressed as 0.08%. |
| United Kingdom (Scotland) | 5.00% | Scotland lowered to 50 mg/100 ml in 2014. |
| Australia | 5.00% | Full licence 0.05%. Learner/probationary/heavy vehicle drivers must be 0.00%. |
| Canada | 8.00% | Federal Criminal Code 0.08%. Most provinces issue 0.05% warn-range suspensions. |
| New Zealand | 5.00% | 50 mg/100 ml. Drivers under 20 must be 0.00%. |
| Ireland | 5.00% | 50 mg/100 ml. Novice/learner/professional drivers 0.02%. |
| Germany | 5.00% | 0.05% general. 0.03% if accident or impaired behaviour. 0.00% under 21 or first 2 years licensed. |
| France | 5.00% | 0.05% general. 0.02% novice drivers (first 3 years). |
| Spain | 5.00% | 0.05% general. 0.03% novice and professional drivers. |
| Italy | 5.00% | 0.05% general. 0.00% novice (first 3 years), under 21, and professional. |
| Netherlands | 5.00% | 0.05% general. 0.02% novice drivers (first 5 years). |
| Sweden | 2.00% | Very strict 0.02%. Aggravated DUI at 0.10%. |
| Norway | 2.00% | 0.02% — one of the strictest in Europe. |
| Finland | 5.00% | 0.05% general. Aggravated DUI at 0.12%. |
| Japan | 3.00% | Very strict — 0.03% triggers criminal penalty. Higher BAC means severe punishment. |
| South Korea | 3.00% | Lowered to 0.03% in 2019. Licence revoked at 0.08%. |
| India | 3.00% | 30 mg/100 ml. Strict enforcement in metros. |
| Brazil | Zero tolerance | Effectively zero tolerance (Lei Seca). Trace limit ~0.02 g/L (~0.002%). |
| Mexico | 8.00% | 0.08% nationwide. Mexico City Hoy No Circula 0.04% for taxis. |
| South Africa | 5.00% | 0.05% general, 0.02% professional. New zero-tolerance proposals pending. |
| United Arab Emirates | Zero tolerance | Zero tolerance. Any alcohol while driving is criminal. |
| Saudi Arabia | Zero tolerance | Alcohol consumption is illegal. Zero tolerance. |
Limits accurate to time of publication. Verify current law before driving in any jurisdiction.
Understanding BAC and the Widmark Formula
Blood alcohol content (BAC), sometimes called blood alcohol concentration, measures the amount of ethanol in your bloodstream as a percentage by volume — typically grams of alcohol per 100 millilitres of blood. In most of the world it is reported as a decimal such as 0.08% or in milligrams per 100 millilitres of blood (80 mg/100 ml), which are mathematically the same number. BAC is the single most important physiological measure for understanding impairment, legal driving status, and personal safety after consuming alcohol.
The Widmark formula, developed by Swedish physician Erik Widmark in 1932, remains the forensic gold standard for estimating BAC from drink intake. It links four variables — grams of alcohol consumed, body weight, gender-adjusted body water (the "r factor"), and hours since drinking — into a single tractable equation. Modern toxicologists, police investigators, and harm-reduction educators all still rely on Widmark when a blood or breath test is not available. Our calculator implements the same equation, layers on country-specific legal limits, and adds a food-intake adjustment to reflect modern absorption research.
Why does this matter? Because BAC determines whether you are legally allowed to drive, how impaired your motor and cognitive functions are, and how quickly your body can clear the alcohol. A 160-pound male drinking three standard beers in an hour reaches roughly 0.06% BAC — under the US 0.08 limit but over the limit in most of Europe, Scotland, Australia, and Japan. The same three beers in a 130-pound female push BAC closer to 0.09%, which is over the limit in virtually every country in the world. Knowing your number, and the local legal threshold, is the foundation of safe drinking.
The Widmark Formula Explained
BAC % = (A × 5.14 / W / r) − (0.015 × hours)
- A (grams of alcohol): Calculated from drink volume and alcohol-by-volume (ABV). A US standard drink contains ~14 g of pure alcohol — that is 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirit.
- W (body weight): Larger bodies have more blood and tissue to dilute alcohol, so the same drinks produce a lower BAC. Our calculator accepts both pounds and kilograms and converts internally.
- r (Widmark constant): 0.73 for males, 0.66 for females. Approximates the fraction of body mass that contains water, which is where alcohol distributes. Women generally have higher body fat and lower water content, which raises BAC per drink.
- 0.015 × hours: Average alcohol metabolism rate. Your liver clears about 0.015% BAC per hour — equivalent to roughly one standard drink per hour. This rate cannot be reliably accelerated by food, water, coffee, or exercise.
- 5.14 constant: Converts the imperial-unit equation to a percentage. The constant absorbs the conversion factors between grams, pounds, and the volume of distribution.
Why Individuals Vary So Much
The Widmark formula is an average. Your real BAC can vary by ±20-30% from the calculator output based on factors the formula does not capture:
Body composition
Body fat does not contain water and therefore does not dilute alcohol. Two people with the same weight but different body fat percentages will reach different BACs.
Genetics & ethnicity
People of East Asian descent often have reduced ALDH2 enzyme activity, which slows acetaldehyde metabolism and can change the apparent BAC curve.
Hormonal cycle
Women have a slightly higher BAC at the same drinks during the premenstrual phase, because body water composition varies through the cycle.
Medications
Many drugs — including antibiotics, antidepressants, and acid reducers — interact with alcohol metabolism in ways that can dramatically change BAC behaviour.
Recent eating
Food slows gastric emptying, which slows alcohol absorption and lowers peak BAC by 10-20%. Our calculator applies this adjustment when you tick "with food."
Drinking pace
Rapidly consumed drinks produce a sharper, higher peak BAC than the same alcohol spread over hours. The Widmark formula models steady absorption.
How to Use This Calculator
- 1. Enter your personal info: Pick your gender (Widmark uses this to set the r-factor), your body weight in pounds or kilograms, and how many hours have passed since your first drink.
- 2. Toggle the food setting: If you ate during or before drinking, leave "with food" selected. The calculator applies a 15% peak-BAC reduction to reflect slower absorption.
- 3. Pick your country: The dropdown sets the legal limit used in the over/under check and time-to-legal countdown. Default is the US 0.08% standard.
- 4. Add your drinks: Tap Add Beer, Add Wine, Add Spirit, or Custom to log each drink. Adjust the size and ABV to match what you actually consumed — craft beers can be 8-12%, restaurant wine pours are often 6 oz, and home pours of spirits run heavy.
- 5. Calculate and read the dial: The animated gauge shows your current BAC in colour-coded zones. Below it you will see whether you are over the legal limit, your peak BAC, the time until you reach 0.00%, and the time until you are under the local driving limit.
Real-World Use Cases
Designated Driver Planning
Before a night out, the designated driver can model what one or two non-alcoholic drinks plus a single light beer would do to their BAC over the evening — typically staying safely below every legal limit. Pair with our Calorie Intake Calculator to factor the food you will eat before driving home.
Morning-After Safety Check
Heavy night out? Plug in your last estimated peak BAC and the number of hours of sleep to find out whether you are still legally impaired in the morning. A BAC of 0.15 at 1 AM is still 0.04 at 9 AM — over the limit in Scotland and most of Europe.
Hospitality & Bar Staff
Bartenders and event coordinators use this tool to give patrons a realistic answer when asked "am I ok to drive?" — and to encourage rideshares when the answer is no. Pair with our BMR Calculator for staff training on body-composition factors that change BAC.
International Travel
Driving abroad? Our country dropdown shows the local limit and lets you adjust your drinking plan accordingly. A drink that is legal in the US may put you well over the limit in Norway, Sweden, Japan, or India. Cross-reference your trip with our TDEE Calculator to plan your overall daily energy and alcohol intake.
Pro Tips for Safer Drinking
- • Eat before and during drinking: A meal with fat and protein slows absorption and lowers peak BAC by 10-20%. The infamous "line your stomach" advice is real.
- • Alternate alcohol with water: One full glass of water between each drink slows your drinking pace, keeps you hydrated, and reduces the next morning's hangover. It does not change BAC, but it changes how you feel.
- • Your BAC keeps rising after your last drink: Alcohol absorbs into the bloodstream for 30-90 minutes after consumption. The drink you just finished is not the drink you are currently feeling. Pace yourself accordingly.
- • Designate a driver before you start drinking: Decisions made sober are better than decisions made at 0.05%. Pick the driver before the first drink.
- • Count standard drinks, not glasses: A pint of 8% IPA is 1.6 standard drinks. A 6 oz pour of 14% wine is 1.4 standard drinks. A home-poured G&T can easily be 2 standard drinks in a single glass.
- • Time, not coffee, is the only sobering agent: Coffee makes a drunk person an awake drunk person. The liver clears alcohol at a fixed rate. Plan around it.
- • When in doubt, do not drive: The cost of a taxi or rideshare is always less than the cost of a DUI, a crash, or a life. If you are even slightly unsure, do not drive.
Standard Drink Sizes Around the World
The concept of a "standard drink" varies by country, which makes comparing intake across borders confusing. Here are the most common standards:
- • United States: 14 g of pure alcohol — 12 oz of 5% beer, 5 oz of 12% wine, 1.5 oz of 40% spirit.
- • United Kingdom: 8 g per "unit" — half a pint of 4% beer is 1 unit, a 175 ml glass of 12% wine is 2.1 units.
- • Australia: 10 g per standard drink — a typical 285 ml "pot" of 4.8% beer is one standard drink.
- • Canada: 13.6 g per standard drink — close to the US figure.
- • Japan: Uses "go" for sake (180 ml at ~15% ABV = ~22 g alcohol) but no formal "standard drink" in marketing.
- • European Union: Most countries use 10 g per standard drink, though the WHO defines it as 10 g globally.
A Note on Accuracy
This calculator is built on widely accepted physiological constants and the same Widmark formula used by forensic toxicologists. Its output is an educated estimate, not a measurement. Your real BAC at any moment depends on dozens of variables the formula cannot see — and even a calibrated breathalyzer can vary by ±0.01% between readings. Use this tool to plan, learn, and have a more honest conversation with yourself about alcohol. Do not use it to decide whether to drive. The only safe BAC for driving is 0.00%.
What People Are Saying
“I keep this tab open at the bar. When a regular asks if they're 'ok to drive home,' I plug in their numbers and we both look at the answer together. Half the time it convinces them to grab an Uber, which is exactly the point.”
“Japan's 0.03 limit is one of the strictest, and tourists rarely realise. I send my visiting students this link before they head out. The country-specific limits saved one of them from a much worse weekend.”
“Sweden's 0.02 limit makes most BAC calculators useless for our drivers. This one handles it correctly and shows the time-to-legal countdown. I now reference it in my harm-reduction workshops with hospitality staff.”
“Running corporate events with open bars in Australia means walking the line between fun and the 0.05 limit. The peak BAC versus current BAC distinction has stopped more than one guest from making a poor decision at the end of the night.”
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Final Reminder
This BAC calculator is an estimate based on the Widmark formula and idealized metabolism. Many factors affect your actual BAC — food, medication, body composition, hydration, time of day, hormonal cycle, genetics, drinking pace, and more.
Never drive after drinking. If you have any doubt, call a ride. The cost of a taxi is always less than a DUI, a crash, or a life.
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