Alcohol Unit Calculator

An alcohol unit calculator converts drink types and quantities into UK alcohol units and an estimated blood alcohol concentration (BAC). One UK unit equals 10ml (8g) of pure alcohol — the amount the average adult liver can process in one hour. BAC (blood alcohol concentration) measures the percentage of alcohol in your bloodstream and determines your level of impairment. Our alcohol unit calculator uses the validated Widmark formula to estimate BAC from total alcohol consumed, body weight, and gender, giving you a clear picture of how much you have drunk and how it affects your body.

1. 1. Enter Your Personal Details: Select your gender and enter your body weight in kg. These are used by the Widmark formula to estimate your blood alcohol concentration — heavier individuals have a lower BAC for the same amount of alcohol.
2. 2. Add Your Drinks: Select each drink type from the 18 presets (pints, wine glasses, spirits, alcopops, and more) and enter the quantity. Use the custom drink option for any beverage by entering the volume in ml and ABV%. Add as many drinks as needed.
3. 3. View Units, BAC, and Sober Time: Click Calculate Units & BAC to see your total UK units, estimated BAC with category, a visual BAC gauge with the UK drink-drive limit marked, a per-drink breakdown, and estimated hours until sober.

• UK Alcohol Units: UK Units = (Volume in ml × ABV%) ÷ 1000. For example, a pint of 4% lager (568ml): (568 × 4) ÷ 1000 = 2.27 units. A single spirit (25ml, 40%): (25 × 40) ÷ 1000 = 1.0 unit exactly.
• Widmark BAC Formula: BAC% = (Alcohol in grams ÷ (Body weight in kg × r × 10)), where r = 0.68 for males and 0.55 for females. The r factor accounts for the different proportion of body water between genders. Alcohol in grams = Volume (ml) × (ABV% ÷ 100) × 0.789 (ethanol density).
• Alcohol Metabolism Rate: The liver metabolises approximately 0.015% BAC per hour on average (roughly 1 UK unit per hour). This rate varies between individuals based on liver enzyme activity, food intake, and other factors. Our alcohol unit calculator uses the average rate for estimation.

• Total UK Units: The sum of alcohol units across all drinks entered. The NHS recommends no more than 14 units per week for both men and women.
• Estimated BAC (%): Blood alcohol concentration as a percentage (g/100ml). The UK drink-drive limit is 0.08% (80 mg/100ml). Results are estimates — actual BAC varies with food, metabolism, and other factors.
• BAC Category: Your estimated impairment level: Sober, Mild, Moderate, Significant, Severe, or Dangerous — with a description of typical effects at that BAC level.
• Hours to Sober: Estimated time for your BAC to return to zero at the average metabolism rate of 0.015% per hour. This is an estimate — do not rely on it to decide whether to drive.

BAC estimates from our alcohol unit calculator are based on the Widmark formula and are approximations only. Actual BAC is affected by food intake (food slows alcohol absorption), individual metabolism rates, medications, hydration, and other factors. The Widmark formula has a standard error of approximately ±20%. Never use this tool to decide whether it is safe to drive — if you have consumed any alcohol, the safest choice is not to drive. The UK drink-drive limit is 0.08% BAC (80 mg/100ml blood).