How drunk are you really after three beers? Are you over the legal limit? When can you drive again? Instead of typing in every glass's volume and ABV, the standard-drink method gives you a usable BAC estimate in 30 seconds.
This guide explains how the Blood Alcohol Estimator uses the Widmark formula, what BAC and promille really measure, and which legal limits apply in the US, UK and EU.
What is a standard drink?
A US standard drink contains exactly 14 grams of pure alcohol — regardless of what's in the glass. That convention makes the math doable in your head.
| Drink | Serving | ABV |
|---|---|---|
| Beer | 12 oz (350 ml) | ~ 5% |
| Wine | 5 oz (150 ml) | ~ 12% |
| Spirits | 1.5 oz (44 ml) | ~ 40% |
Watch out: a 16 oz craft IPA at 7% is closer to 2 standard drinks, and a generous wine pour easily counts as 1.5. UK units are smaller (8 g of alcohol) — see the Alcohol Unit Calculator.
The estimation formula
The estimator plugs your standard drinks into the Widmark formula directly:
BAC (%) = (drinks × 14 g) / (weight × r) × 0.1 − 0.015 × hours
r = 0.68 (male) | r = 0.55 (female)
The r factor reflects body water content. Women on average have less body water, so the same alcohol load yields a higher BAC.
Worked example
| Step | Calculation |
|---|---|
| Input | Male, 80 kg (176 lb), 4 drinks, 1 hour |
| Alcohol (g) | 4 × 14 = 56 g |
| Raw BAC | 56 / (80 × 0.68) × 0.1 = 0.103% |
| After 1 h | 0.103 − 0.015 = 0.088% (≈ 0.88‰) |
| Time to sober | 0.088 / 0.015 = ~ 5.9 hours |
BAC vs. promille
BAC in % (US) and promille (Europe) measure the same thing in different units:
0.08% BAC = 0.8‰ | 0.05% BAC = 0.5‰ | 0.02% BAC = 0.2‰
Rule of thumb: BAC × 10 = promille. The result panel shows both values.
Driving limits around the world
| Country | Limit | Notes |
|---|---|---|
| USA (most states) | 0.08% | 0.04% commercial, 0.00% under 21; Utah: 0.05% |
| UK (England, Wales, NI) | 0.08% | Scotland: 0.05% |
| Germany / Austria | 0.05% (0.5‰) | 0.03% with signs of impairment, 0.00% new drivers |
| Sweden, Norway, Poland | 0.02% | A single drink may put you over |
Hourly elimination
The body clears alcohol at roughly 0.015% BAC per hour (~ 0.15‰). The rate is essentially constant — coffee, cold showers and exercise do not speed it up. Only time does.
Practical takeaway: if you go to bed at BAC 0.15%, after eight hours of sleep you're still at 0.03% — morning-after residual is real.
Estimate your BAC now
Sex, weight, drinks, hours — done. BAC, promille and time-to-sober at a glance.
Run the free estimate →Where the estimate gets fuzzy
Empty stomach
On an empty stomach alcohol absorbs faster — peak BAC is higher. A heavy meal can reduce the peak by 20–30%.
Medications
Pain relievers, antibiotics and several antidepressants interact with alcohol and amplify its effects. Check the label.
Genetics & liver health
ADH gene variants (common in East Asian populations) and liver disease slow elimination significantly.
Related calculators
Need precise per-drink input (volume × ABV)? Use the more detailed Blood Alcohol Calculator. For weekly consumption tracking in UK units, see the Alcohol Unit Calculator. And for the long-term picture: Life Expectancy Calculator.
Bottom line
The standard-drink method is precise enough to answer the only question that matters in the moment: "can I drive?" If the estimator returns anything above your local limit, the answer is no. When in doubt — one drink fewer, one hour more. Try the Blood Alcohol Estimator for your situation.