BAC Calculator

What Is Blood Alcohol Concentration (BAC)?

Blood Alcohol Concentration, or BAC, is a simple way to measure how much alcohol is in your bloodstream at a given moment. It's written as a percentage, like 0.05% or 0.08%, which tells you what portion of your blood is pure alcohol. A BAC of 0.08%, for example, means that 0.08 grams of alcohol are present in every 100 milliliters of your blood.

This number matters because it's the closest thing we have to a direct measure of how alcohol is affecting your body at any point in time. It's used by doctors to judge intoxication, by police to enforce drink-driving laws, and by everyday people who just want a clearer sense of how many drinks is too many. This free BAC calculator lets you estimate your own blood alcohol concentration using your drinks, your body weight, your sex, and how much time has passed since you started drinking.

How This BAC Calculator Works: The Widmark Formula

This tool is built on the Widmark formula, the same math that toxicologists, researchers, and most professional BAC charts have relied on since the 1930s. In plain language, the formula looks at three things: how much pure alcohol you drank, how much of your body that alcohol has to spread through, and how much time your liver has had to break some of it down.

The full formula is: BAC = (grams of alcohol ÷ (body weight in grams × distribution ratio)) × 100 − (elimination rate × hours passed). The 'distribution ratio' accounts for the fact that alcohol mixes into body water, and men and women have different average amounts of body water relative to body fat, which is why the calculator asks for biological sex. The 'elimination rate' is simply how fast the average liver clears alcohol from the blood, which this calculator sets at 0.015% per hour, a widely used average.

Every drink you add is first converted into grams of pure alcohol using its volume and ABV (alcohol by volume) percentage, since a large low-strength beer and a small high-strength shot can contain a very similar amount of actual alcohol. Add up your drinks, enter your weight and how long ago you started drinking, and the calculator does the rest instantly.

Reading Your BAC Result and Impairment Stage

A single BAC number is useful, but it's more meaningful with context, which is why this calculator also shows an impairment stage next to your result. These stages are based on widely published reference ranges used in road-safety and health education material.

• 0.00-0.02%: Minimal to no measurable effect for most adults.
• 0.02-0.05%: Mild relaxation, slightly lowered alertness.
• 0.05-0.08%: Noticeably reduced coordination and reaction time — this range covers many countries' legal driving limits.
• 0.08-0.15%: Clear loss of muscle control, slurred speech, and impaired judgment.
• 0.15-0.30%: Severe impairment, poor balance, blurred vision, risk of blackout.
• 0.30%+: A medical emergency range — risk of alcohol poisoning and loss of consciousness.

What Counts as "One Drink"? Standard Drink Sizes Explained

One of the most common mistakes people make when guessing their own BAC is assuming every drink counts the same. It doesn't. A 'standard drink' in most countries contains around 14 grams of pure alcohol, but the volume that adds up to differs hugely between drink types. A 12 oz (355 mL) regular beer at 5% ABV, a 5 oz (148 mL) glass of wine at 12% ABV, and a 1.5 oz (44 mL) shot of spirits at 40% ABV all land close to one standard drink, even though they look nothing alike in the glass.

This calculator doesn't force you to think in 'standard drinks' at all — you enter the actual volume and ABV of what you drank, whether that's a pint of craft beer, a strong cocktail, or a glass of champagne, and it converts everything into grams of alcohol behind the scenes. The quick-add buttons are there to save time if you had something typical, and you can always adjust the volume or ABV to match the real label on your bottle or can.

Why BAC Isn't the Same for Everyone

Two people can drink the exact same amount and end up with very different BAC levels. Body weight is the biggest factor here — a heavier person has more total body water for the alcohol to spread into, which dilutes it and generally results in a lower BAC than a lighter person who drank the same amount. This is exactly why the calculator asks for your weight before estimating anything.

Biological sex plays a role too, mostly because of average differences in body water percentage and how the stomach enzyme that breaks down alcohol behaves, which is reflected in the different distribution ratio used for each option. Beyond what this calculator can measure, real-world BAC is also affected by things like how much food was in your stomach, how quickly you drank (all at once versus spread over several hours), medication, liver health, and general tolerance — none of which a math formula alone can fully capture, so always treat the result as a close estimate rather than an exact reading.

How Long Does Alcohol Stay in Your System?

Once you stop drinking, your liver keeps clearing alcohol from your blood at a fairly steady pace, roughly 0.015% BAC per hour for the average adult — regardless of coffee, cold showers, or exercise, none of which speed up the process despite popular belief. That means if your BAC is sitting at 0.08%, it takes roughly five to six hours of doing absolutely nothing else for it to reach zero.

This calculator's 'Time Until Sober' and 'Time Until Under Legal Limit' results use exactly this elimination rate to project forward from your current estimated BAC. The BAC timeline chart above shows the same idea visually — a rise while you're drinking, followed by a steady straight-line decline back down to zero as your liver does its work.

Legal Drink-Driving Limits Around the World

Legal BAC limits for driving vary a lot by country and even by region within a country. In most of the United States and the UK (outside Scotland), the standard limit is 0.08%, while commercial drivers in the U.S. face a stricter 0.04% limit and drivers under 21 face a near-zero 0.02% limit in most states. Scotland, along with most of continental Europe, sets the bar lower at 0.05%, and countries like Sweden, Norway, and India apply even stricter limits around 0.02-0.03%.

This calculator lets you pick a region from the dropdown to see how long it would take your estimated BAC to fall under that specific threshold. Keep in mind that these limits describe when a country's law considers you legally impaired to drive, not when it's actually safe to be behind the wheel — reaction time and judgment can be affected well below any of these numbers, which is why zero is always the truly safe answer.

Who Uses a BAC Calculator?

People reach for a BAC calculator for a lot of different reasons. Some want a rough sense of how their body processes alcohol so they can plan a safer night out — knowing roughly how many hours it takes to clear a few drinks helps with deciding when to stop or how long to wait before getting behind the wheel the next morning. Bartenders, event hosts, and health educators use it as a teaching tool to show how weight, drink strength, and time all interact. Students studying biology, nursing, or toxicology use it to understand how the Widmark formula actually works with real numbers instead of just reading about it in a textbook.

Whatever the reason, the goal of this tool is the same: turn a set of drinks, a body weight, and a bit of time into a clear, honest estimate — not a certainty, but a genuinely useful reference point.

A Note on Accuracy and Responsible Use

This calculator uses the Widmark formula, a respected and widely used estimation model, but it is still an estimate, not a lab test. Real BAC can be higher or lower than the number shown here depending on factors this formula can't measure directly — how fast you drank, whether you ate beforehand, your individual metabolism, medications, and general health all shift the real number in ways a simple calculator cannot.

For that reason, this tool should never be used to decide whether it is safe or legal to drive, operate machinery, or make any other decision where being wrong has serious consequences. The only BAC that guarantees safe driving is 0.00%. If you've been drinking at all, the responsible choice is a taxi, a rideshare, public transport, or a sober friend — not a number on a screen. This calculator is provided for general education and curiosity, not as medical, legal, or safety advice.