Blood Alcohol Content (BAC) Calculator
Estimate your BAC with correct legal limits for your region — including UK Scotland (0.05%) vs England & Wales (0.08%). Widmark formula.
BAC Calculator
Legal driving limit: 0.08% BAC
Estimated BAC
0.043%
Estimate only — never drive after drinking. Individual metabolism varies. A certified breathalyser is the only reliable test.
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The BAC calculator estimates your blood alcohol content using the Widmark formula — the same model used by law enforcement and health researchers worldwide. Select your region first: the legal driving limit differs between Scotland (0.05%), England & Wales (0.08%), the US and Canada (0.08%), and Australia and most of Europe (0.05%). Enter your drinks, weight, biological sex, and hours since drinking started — the result is colour-coded against your region's specific limit. Scotland lowered its limit from 0.08% to 0.05% in December 2014, making it the strictest drink-drive limit in the UK. This means a 70 kg male who is under the limit in England could be over the limit in Scotland after the same number of drinks. If you regularly travel between the two, selecting the correct region matters. This calculator is a planning and awareness tool — not a substitute for a breathalyser or medical test. Individual metabolism varies by ±20%. Never make a driving decision based solely on a calculator estimate. If you have consumed any alcohol, the safest choice is always not to drive.
Using This Blood Alcohol Content (BAC) Calculator
The Blood Alcohol Content (BAC) Calculator is designed to give you an accurate answer in seconds. Follow these steps:
- 1Select your region using the pill buttons at the top — US/Canada, UK England & Wales, UK Scotland, Australia/Europe, or Other. This sets the correct legal driving limit your result is checked against.
- 2Enter the number of standard drinks consumed. One standard drink = one 355ml beer (5%), one 148ml glass of wine (12%), or one 44ml shot of spirits (40%).
- 3Enter your body weight and choose kg or lbs using the toggle.
- 4Select your biological sex. Males use a factor of 0.68 and females 0.55 — reflecting differences in total body water, which affects how alcohol is distributed.
- 5Enter how many hours have passed since you started drinking. The body metabolises approximately 0.016% BAC per hour.
- 6Your estimated BAC appears instantly — colour-coded green (under limit), amber (approaching limit), or red (over limit) against your region's legal threshold. The estimated time to sober is shown below.
No account or sign-up required. All calculations run locally in your browser — nothing is stored or transmitted to any server.
What Your Result Means
BAC (%) = (Drinks × 14) ÷ (Weight_kg × Gender Factor × 10) − (0.016 × Hours)
Formula: BAC = (Drinks × 14 ÷ (Weight × Gender Factor)) − (0.016 × Hours) The Widmark formula calculates BAC based on: - Alcohol consumed: each standard drink contains 14 grams of pure alcohol (the US standard; one 355ml beer, 148ml wine, or 44ml spirits at standard strength) - Body weight: heavier people have more body water to dilute alcohol - Gender factor: males use 0.68 (68% of body weight is water); females use 0.55 (due to proportionally lower total body water) - Metabolism: the body metabolises alcohol at approximately 0.016% BAC per hour regardless of body weight Example: 75 kg male, 3 drinks over 2 hours. BAC = (3 × 14 / (75 × 0.68)) − (0.016 × 2) = 42 / 51 − 0.032 = 0.824 − 0.032 = 0.792... wait, that is BAC in g/dL ÷ 10 = 0.079% Actual factors that affect BAC beyond this formula include: food consumed (slows absorption by ~50%), drinking speed (faster drinking raises peak BAC), medication, and individual metabolic variation of ±20%.
Questions People Ask
What is the legal BAC limit for driving?
Legal limits vary significantly by region. UK — Scotland: 0.05% (50 mg/100ml) — the strictest limit in the UK, introduced in December 2014. UK — England & Wales: 0.08% (80 mg/100ml). United States: 0.08% federal standard; 0.04% for commercial drivers. Canada: 0.08% (0.05% in some provinces triggers administrative penalties). Australia: 0.05% for fully licensed drivers; 0.00% for learners and P-platers. Germany and most of mainland Europe: 0.05%. Sweden, Norway: 0.02%. Japan: 0.03%. Czech Republic, China: 0.00%. Always check the current local limit — this calculator lets you select your region to check against the correct threshold.
How long does it take to sober up after drinking?
The body metabolises approximately 0.016% BAC per hour. If your BAC peaks at 0.10%, it takes around 6 hours to return to 0.00%. There is no way to speed up this process — coffee, cold showers, and food do not accelerate alcohol metabolism. Food slows absorption (reducing peak BAC) but does not change the rate of elimination. The only remedy for elevated BAC is time.
What counts as a standard drink?
A standard drink contains approximately 14 grams of pure alcohol in the US. This equals: one 355 ml can of regular beer (5% ABV), one 148 ml glass of wine (12% ABV), or one 44 ml shot of spirits (40% ABV). Note that standard drink definitions vary by country: the UK unit is 8 grams of alcohol; Australia's standard drink is 10 grams. Craft beers and strong wines often contain 1.5–2+ standard drinks per serving despite being a single glass.
Does eating before drinking lower your BAC?
Yes — significantly. Eating before or during drinking slows gastric emptying, which delays alcohol absorption and reduces peak BAC by up to 50%. High-fat and high-protein foods are most effective at slowing absorption. Eating does not reduce total alcohol processed or prevent eventual intoxication — it just spreads the absorption out over a longer period, producing a lower and later peak BAC.
Is the BAC calculator accurate?
The Widmark formula produces estimates accurate to within ±15–25% for most people. Individual variation in metabolism, tolerance, medication interactions, and hydration level all affect actual BAC. This calculator should never be used to make a driving decision. The only reliable way to know your BAC is a certified breathalyser or blood test. If you have consumed any alcohol, the safest choice is always not to drive.