Understanding UK Alcohol Units
The concept of the alcohol "unit" was introduced in the UK in 1987 to give people a simple way to measure their alcohol intake. One unit equals 10ml or 8g of pure alcohol — the amount the average adult liver can process in about one hour. This metric underpins NHS alcohol guidelines and enables straightforward comparison between drinks of different strengths and volumes.
Why ABV and Volume Both Matter
A common misconception is that a "glass of wine" is always one unit. In reality, a small 125ml pour of 13% wine contains 1.6 units, while a large 250ml glass of the same wine contains 3.25 units. Similarly, a pint of 3.5% session beer contains 2.0 units while a pint of 8% craft IPA contains 4.5 units. The formula is unambiguous: multiply volume in millilitres by ABV percent and divide by 1000.
NHS Guidelines and Risk Categories
The NHS advises both men and women to drink no more than 14 units per week on a regular basis. This represents the approximate threshold below which the weekly risk of alcohol-related illness remains low. The guidelines also specify spreading drinking over at least three days rather than concentrating units in one or two sessions — "binge drinking" carries acute risks independent of total weekly consumption.
Risk categories increase progressively: 14-21 units/week is "increasing risk," 21-35 units is "high risk," and above 35 units per week is "very high risk," associated with significant probability of liver disease, cardiovascular problems, and alcohol dependency over time.
Blood Alcohol Concentration and the Widmark Formula
BAC estimation uses the Widmark formula, developed by Erik Widmark in the 1930s. The calculation accounts for body weight and sex because larger people dilute alcohol into more body water, and women on average have proportionally less body water than men of the same weight. The formula subtracts 0.015% BAC per hour to account for liver metabolism. Important caveats: food consumption slows absorption significantly, individual metabolic rates vary, and the formula assumes complete absorption. The result is an educational estimate, not a legal measurement.
Calories in Alcohol
Alcohol is calorie-dense at 7 kcal/gram — more than protein or carbohydrates (both 4 kcal/g), though less than fat (9 kcal/g). A unit of alcohol (8g) contributes roughly 56 calories from the alcohol itself. Beer and wine also contain carbohydrates that add further calories — a pint of 5% beer typically totals 200-250 calories. Regular drinking can represent a substantial hidden caloric load, particularly relevant for weight management.