Blood Alcohol Calculator (BAC)
Enter your drinks and see an estimated BAC — an educational guide, never a green light to drive.
Sex
Sex sets the Widmark r factor (0.68 male / 0.55 female, population averages).
Drinks
Add each drink you had. Presets use typical serving sizes; choose Custom to enter your own volume and ABV.
Estimated current BAC
≈ 0.00 % — alcohol has likely been metabolized.
Potentially life-threatening range — seek emergency help immediately.
Legal BAC limits vary by country — e.g. 0.03% in Korea and Japan, 0.05% across much of the EU, 0.08% in the US and UK, and zero for novice or commercial drivers in many places.
This is a rough statistical estimate from the Widmark formula. Real BAC depends on food, metabolism, medication and health, and can be higher than shown. Never use this tool to decide whether to drive.
How this calculator turns your drinks into a BAC estimate
Blood alcohol content is normally only measured with a breathalyzer or a blood draw, but most people want a rough sense of where they stand well before either is on hand — at a party deciding whether to open one more beer, the morning after wondering if last night is still in their system, or a student working through the forensic-toxicology math behind drunk-driving law. This calculator answers that "roughly where am I" question using the Widmark formula, the model used in textbooks and expert testimony since the 1930s. Every number it produces is an educational estimate built from population averages, not a diagnostic reading — it cannot replace an actual test, and it should never decide whether you, or anyone else, is fit to drive.
What each field actually changes
- Sex sets the Widmark distribution ratio, r — 0.68 for men and 0.55 for women. This factor stands in for the fraction of body weight that is water, which is where alcohol distributes; women have a lower average body-water fraction, so the same dose spreads through less volume and produces a higher BAC.
- Body weight is the tank size alcohol dilutes into. Doubling body weight roughly halves peak BAC for identical drinks — this is the single biggest reason two people at the same party can feel very differently after the same number of drinks.
- Drinks determine total grams of pure ethanol consumed. Each preset (beer, wine, soju, spirits) uses a realistic serving volume and ABV; choosing "Custom" lets you enter any volume and ABV, useful for craft beer, cocktails, or a poured-at-home measure that doesn't match a standard serving.
- Hours since you started drinking is how long your liver has had to metabolize alcohol at a fixed clearance rate. Longer elapsed time subtracts more from the peak figure, down to a floor of 0.00%.
The Widmark math, in plain terms
Step 1 — grams of alcohol per drink:
grams = volume (mL) × (ABV ÷ 100) × 0.789 (ethanol's density in g/mL)
Step 2 — peak BAC:
peak % = total grams ÷ (body weight in grams × r) × 100
Step 3 — current BAC:
current % = peak % − (0.015 × hours elapsed), floored at 0.00%
That last constant, 0.015% per hour, is the average rate a healthy liver oxidizes alcohol — roughly one standard drink's worth of ethanol every 60–90 minutes. It is treated as a straight line here for simplicity, which real elimination only approximates once your body has finished absorbing what you drank.
Three worked examples
Example 1 — a couple of beers, one hour in. Male, 80 kg, two 355 mL beers at 5% ABV, 1 hour since the first sip. Alcohol: 2 × (355 × 0.05 × 0.789) ≈ 28.0 g. Peak: 28.0 ÷ (80,000 × 0.68) × 100 ≈ 0.05%. Current: 0.05% − (0.015 × 1) ≈ 0.04% — inside the 0.03–0.079% band, roughly 26 minutes from dropping under 0.03% and about 2 hours 26 minutes from reading 0.00%.
Example 2 — wine and soju right after the last pour. Female, 60 kg, one 150 mL glass of wine at 12% plus two 50 mL soju shots at 17%, 0 hours elapsed (peak reading). Alcohol: 14.2 g + 13.4 g ≈ 27.6 g. Peak = current: 27.6 ÷ (60,000 × 0.55) × 100 ≈ 0.08% — right at the U.S./U.K. legal threshold, about 15 minutes from dropping under it and roughly 5 hours 35 minutes from 0.00%.
Example 3 — same drinks, most of a night's sleep later. Male, 75 kg, three 355 mL beers at 5%, 8 hours elapsed. Peak comes out to about 0.08% again, but 0.08% − (0.015 × 8) = 0.08% − 0.12% is negative, so the estimate floors at 0.00% — the model treats this person as fully metabolized, illustrating why "I only had three beers" says much less than "three beers, eight hours ago."
Reference tables
| Preset drink | Serving used | ABV | Pure alcohol |
|---|---|---|---|
| Beer | 355 mL (~12 oz can) | 5% | ≈14.0 g |
| Wine | 150 mL (~5 oz glass) | 12% | ≈14.2 g |
| Soju shot | 50 mL | 17% | ≈6.7 g |
| Spirits shot | 44 mL (~1.5 oz) | 40% | ≈13.9 g |
A soju shot carries roughly half the pure alcohol of a beer, wine glass or spirits shot — one reason soju rounds feel deceptively light until several add up.
| Peak BAC | Approx. time back to ~0.00% |
|---|---|
| 0.02% | ~1 h 20 m |
| 0.05% | ~3 h 20 m |
| 0.08% | ~5 h 20 m |
| 0.15% | ~10 h 00 m |
| 0.20% | ~13 h 20 m |
| 0.30% | ~20 h 00 m |
Mistakes that throw the estimate off
- Assuming coffee, cold water or a nap speeds things up. The 0.015%/hour clearance rate is fixed by liver enzyme activity — nothing you do afterward changes its slope.
- Comparing two people's totals directly. Because r and body weight sit in the denominator, identical drinks can land at very different BAC for a lighter person, a woman, or someone who ate nothing beforehand — food intake isn't part of this model at all.
- Entering "0" hours right after the last drink and treating that as a ceiling. Real absorption continues for 30–90 minutes past your last sip, so true peak BAC can run a little higher than a same-moment estimate, especially on an empty stomach.
- Trusting a rounded-down ABV or a "generous" home pour. A restaurant glass or a self-mixed spirit is often larger than the preset serving; switch to Custom and measure honestly instead of relying on a preset that undercounts.
What this model can't see
The Widmark formula is a population-average model, not a personalized one. It does not account for food in your stomach (which slows absorption and lowers the peak), genetic differences in alcohol-dehydrogenase activity, medication interactions, chronic drinking history, illness, or the early absorption phase where BAC is still climbing. Two people who enter identical numbers can have a real BAC that differs by 20–30% either direction from this estimate. Use it to understand roughly how the math works and to get a ballpark sense of your evening — never as a green light to get behind the wheel. If there is any doubt, the only safe assumption is to wait, arrange another way home, and let more time pass than the number on screen suggests.
Sources & further reading
Frequently asked questions
What is the Widmark formula and how is BAC estimated?
The Widmark formula is the classic way to estimate blood alcohol content (BAC). This blood alcohol calculator adds up the pure ethanol in your drinks in grams (A), then computes peak BAC = A ÷ (body weight in grams × r) × 100, where r is a body-water constant (0.68 for men, 0.55 for women). It then subtracts the alcohol your liver has already burned off — about 0.015% per hour — to estimate your current BAC. It is the same Widmark formula calculator method used in textbooks, applied entirely in your browser.
How accurate is this, and why can't I trust it to decide to drive?
Treat every number here as a rough educational estimate, not a measurement. Real BAC varies widely with food in your stomach, how fast you drank, body composition, liver health, medication and even the day. Two people of the same weight can end up far apart, and your true BAC can be higher than this calculator shows. Only a breathalyzer or blood test measures your actual level — so never use a BAC calculator to decide whether it is safe to drive. If you have been drinking, do not drive.
How long does it take for alcohol to leave your system?
Your body clears alcohol at a fairly steady rate of roughly 0.015% BAC per hour, and only time lets the liver do this work. Coffee, cold showers, water, food and fresh air can make you feel more alert but do not speed up how fast alcohol leaves your system. This calculator shows an estimated time until your BAC falls below common limits and back to about 0.00%, but the safest assumption is always to allow more time than the estimate suggests.
What are the legal BAC limits around the world?
Legal driving limits differ by country: about 0.03% in South Korea and Japan, 0.05% across much of Europe, and 0.08% in the United States and the United Kingdom. Many places set a zero or near-zero limit for novice, young or commercial drivers. Because the threshold that counts as "over the limit" depends on where you are, this tool shows reference lines rather than a single pass/fail — and being under a limit still does not mean you are safe to drive.
Is my drinking data sent anywhere?
No. This blood alcohol calculator runs 100% in your browser. Your sex, weight, drinks and hours are used only to compute an estimate on your device and are never uploaded to any server. For convenience they are saved to your browser's localStorage so the form is ready next time, and you can clear them anytime by clearing your site data.