Blood Alcohol Content Calculator
Estimate your BAC from drinks, weight and time elapsed using the Widmark formula, with legal limit comparisons for India, US, UK and Australia.
Quick Tips for a More Accurate Estimate
Features
Why the Widmark Formula Is Still the Industry Standard
Nearly every BAC calculator worth using, from roadside breathalyzer education charts to hospital toxicology references, is built on some version of the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s and still the accepted baseline nearly a century later. The idea behind it is straightforward: alcohol distributes through your body's water content, not your total mass, which is why the formula divides grams of alcohol consumed by body weight multiplied by a distribution constant — 0.68 for men, 0.55 for women — before subtracting however much your body has already metabolized based on time elapsed. It's not a perfect model of any one individual, but as a population-level estimate it's remained the working standard for exactly the reason it was designed: it converts something felt subjectively into a number that's at least directionally trustworthy.
Why "Standard Drinks" Undersell the Real Number
Most simple BAC calculators ask you how many "standard drinks" you had and quietly plug in a fixed 14 grams of alcohol per drink, which is the US definition — the UK uses roughly 8 grams, Australia around 10, and plenty of countries define it differently again. That single assumption alone can shift a result by 30% or more before anything else is even considered, and it gets worse the moment your actual drink doesn't match the assumed size or strength: a double pour of 40% spirits, a 9% imperial stout, or a large glass of 14% wine are nowhere close to the same amount of alcohol as the "one drink" a generic calculator assumes. This tool skips the standard-drink shortcut entirely and calculates directly from ABV, volume and drink count — the beer, wine and spirit presets are just a fast starting point, not the actual basis for the math, so adjusting them to match what you genuinely drank produces a meaningfully more accurate number than picking a category and hoping it's close enough.
What Food, Sex and Body Weight Actually Change
Body weight and sex both change the calculation directly through the distribution constant: a heavier body has more total water volume to dilute the same amount of alcohol into, and the formula's constant for women (0.55) reflects the fact that female bodies typically carry a higher proportion of body fat to water than male bodies of comparable weight, which concentrates alcohol into a smaller effective volume and produces a higher BAC from an identical number of drinks. Food works differently — it doesn't change how much alcohol eventually reaches your bloodstream, only how quickly it gets there, by slowing the rate at which your stomach empties into your small intestine, where most alcohol absorption actually happens. This calculator models that as a modest reduction to peak BAC rather than pretending it prevents intoxication altogether, because a slower peak is a real, measurable effect, but it's a timing shift, not a magic solution.
Two Scenarios Worth Comparing
Someone weighing 60kg and someone weighing 90kg each drink three 12%-ABV wine glasses over two hours. Run through the same formula, the lighter person's peak BAC comes out noticeably higher, purely because the same grams of alcohol are diluted into a smaller volume of body water — same drinks, same timing, meaningfully different result, which is exactly why "three drinks" alone is never a reliable way to estimate impairment across different people.
Someone logs a heavy pour — a 500ml craft beer at 8% ABV, closer to a strong imperial stout than a standard lager — and enters it using the Beer preset without adjusting the numbers. The preset assumes a 5% ABV 355ml serving, meaningfully understating what they actually drank; adjusting the ABV and volume sliders to match the real bottle nearly doubles the calculated grams of alcohol for that single drink compared to leaving the preset untouched.
Why India's Legal Limit Is Stricter Than It Might Seem
India's legal driving limit is 0.03% BAC — noticeably stricter than the 0.08% used across most of the US and England and Wales, and even tighter than Scotland's or Australia's 0.05%. In practical terms, that gap means a BAC level that would still be legal to drive on in several other countries can already be over the line in India, so anyone assuming "one drink is fine" based on limits they've read about elsewhere is working from the wrong number entirely. This calculator defaults its legal-limit reference to India for exactly that reason, while still offering US, UK and Australian limits side by side for comparison if you're traveling or simply curious how the thresholds differ.
Who Actually Uses a BAC Calculator
- Anyone gauging, honestly, whether they're close to a legal limit — before deciding whether to drive.
- People curious how a heavier pour or an empty stomach actually shifts the math compared to what they assumed.
- Students, hosts or event organizers — wanting an educational reference for how alcohol strength and body weight interact.
Pair this with our BMR Calculator and Water Intake Calculator for the broader picture of how your body processes what you consume.
What This Estimate Can't Know
No calculator, this one included, can measure your actual blood alcohol level — only a breathalyzer or blood test can do that, and this tool exists to estimate, not replace one. Individual metabolism varies for reasons a formula can't see: liver function, medication interactions, genetics, tolerance, and even how quickly you drank all shift the real number in ways the Widmark average doesn't capture, which is why feeling sober is not proof of a low BAC and a calculated result under a legal limit is not proof it's safe to drive. Treat every number here as an estimate for awareness and education, and when there's any doubt at all, the only genuinely reliable decision is not to drive.