Read this part first
A BAC calculator is a physiology demonstration, not a breathalyser. Widmark estimates carry individual error of roughly ±20%, frequently more, and the model above knows nothing about what is in your stomach, how fast you drank, your body composition beyond weight, your medications, your liver, or your genetics. It also assumes absorption is complete, so while you are still drinking — and for anywhere from 30 to 90 minutes afterwards — your real BAC may be climbing above what it shows.
So use it to understand how alcohol behaves in a body, and how brutally slow the exit is. Do not use it to decide whether to drive. The only number that is safe for driving is 0.00.
The Widmark equation
Erik Widmark worked this out in Sweden in the 1920s, and it is still the backbone of forensic alcohol calculation. The insight is that alcohol distributes into body water, not body mass, so the concentration you reach depends on how much of you is water:
Everything sensitive lives in r. It is the fraction of your body that alcohol effectively dissolves into, and it averages higher in men because men average a higher proportion of body water. Fat holds very little water, so at the same weight a leaner person reaches a lower BAC than a fatter one — the same reason muscle mass matters more than the scale here.
What a standard drink actually is
The calculator's first three options are all one US standard drink — about 14 g of pure alcohol — which is not obvious from looking at them:
| Drink | Serve | ABV | Alcohol | US std drinks |
|---|---|---|---|---|
| Regular beer | 355 ml (12 oz) | 5% | 14 g | 1.0 |
| Table wine | 148 ml (5 oz) | 12% | 14 g | 1.0 |
| Spirits shot | 44 ml (1.5 oz) | 40% | 14 g | 1.0 |
| Craft IPA | 473 ml (16 oz) | 7% | 26 g | 1.9 |
| Restaurant wine pour | 250 ml | 14% | 28 g | 2.0 |
| Double gin & tonic | 50 ml spirit | 40% | 16 g | 1.1 |
Note also that “standard drink” is not standard between countries: the US uses 14 g, Australia and New Zealand 10 g, the UK unit is 8 g, and Japan uses about 20 g. When you read that men should stay under two drinks a day, the definition matters by nearly a factor of two.
What changes how fast it hits you
Absorption is the variable part of the curve, and it happens mostly in the small intestine rather than the stomach — so anything that slows gastric emptying slows the rise:
- Food. A substantial meal, particularly with fat and protein, can cut peak BAC substantially and push the peak later. On an empty stomach, peak arrives in 30–45 minutes; with food it can take 90 minutes or more.
- Speed. Four drinks in an hour and four drinks over four hours involve identical alcohol and completely different peaks, because elimination has time to work in the second case.
- Concentration and carbonation. Spirits around 20–30% absorb fastest; very high-proof drinks can irritate the stomach lining and paradoxically slow emptying. Carbonation speeds absorption slightly, which is the grain of truth behind champagne's reputation.
- Sex and body composition. Beyond the distribution ratio, women have on average lower gastric alcohol dehydrogenase activity, so less alcohol is broken down before it reaches the bloodstream.
Elimination is a fixed rate — this is the important bit
Once alcohol is in your blood, your liver clears it at an approximately constant rate, because the main enzyme pathway is saturated at almost any drinking BAC. That is why the sober-up chart is a straight line and not a decay curve. Typical values are 0.012–0.020% per hour, with 0.015% used as the population average; regular heavy drinkers metabolise somewhat faster through an induced secondary pathway.
The practical consequence is that nothing speeds it up. Coffee, energy drinks, cold showers, exercise, sleeping, vomiting, greasy food, water — none of them touch the rate. Some of them change how alert you feel, which makes them actively dangerous: a caffeinated drunk is still drunk, and now confident. Only time works, and time works slowly: a BAC of 0.15% needs about ten hours, which is why so many morning-after drivers fail a test.
Legal limits, and why they are not safety limits
| Where / who | Limit |
|---|---|
| Most US states | 0.08% |
| Utah | 0.05% |
| US commercial drivers | 0.04% |
| US drivers under 21 | 0.00–0.02% |
| Most of Europe, Australia | 0.05% |
| Sweden, Norway, Poland, Brazil, Japan | 0.00–0.03% |
These are prosecution thresholds — the point at which the state stops arguing about impairment and simply convicts. Measurable impairment of divided attention, tracking and reaction time appears from around 0.02–0.05%, and crash risk is already elevated below every limit in the table. A calculator that says 0.07% is not telling you that you are safe to drive; it is telling you an estimate, with error bars wide enough to cross the line in either direction.
The rest of the body keeps the tab
Alcohol is 7 kcal per gram, which no macro tracker counts properly — a four-beer evening is roughly 600 kcal that does not appear in your macro split. It also suppresses REM sleep and raises resting heart rate for hours, which is why a night out shows up as a poor recovery score the next morning even when you feel fine. If you want to see that effect on yourself rather than read about it, the HRV calculator explains the marker that moves most, and the sleep calculator covers the timing side.