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Alcohol units explained: what the numbers mean and how to use them

Alcoholic beverages vary widely in both volume and strength. A single measure of spirits, a glass of wine and a pint of beer do not contain the same amount of pure alcohol. To help people compare drinks and monitor consumption, many countries use “units” or “standard drinks” — simplified measures of pure ethanol. Understanding these numbers gives you a clear way to track intake, estimate calories, and compare consumption against local guidance.

How units and grams are calculated

Units are a simple conversion of a drink’s volume and ABV (alcohol by volume). The commonly used UK formula is:

Units = (volume in ml × ABV%) ÷ 1000

This converts the percentage and volume into millilitres of pure ethanol, and then into units where one unit = 10 ml ethanol. For grams, multiply pure ethanol volume by the density of ethanol (~0.789 g/ml): grams = (volume × ABV/100) × 0.789.

US standard drinks and calories

In the United States a “standard drink” is defined as about 14 grams of pure ethanol. Using the grams calculation you can see how many US standard drinks a beverage equals. Alcohol also contributes energy — roughly 7 kilocalories per gram — so it’s common to estimate calories from alcohol as: calories = grams of ethanol × 7. That’s why alcohol can add significant calories even when it doesn’t feel filling.

Why tracking units matters for health

Public health guidance (weekly or daily limits) is often expressed in units or standard drinks. Tracking units helps you evaluate whether your pattern of drinking exceeds recommendations and can guide reductions. It also helps compare different drinks — for example, a large craft beer may contain more units than a small glass of wine.

Practical examples

A 330 ml can of beer at 5% ABV contains: 330 × 0.05 = 16.5 ml ethanol → 1.65 UK units (16.5 ÷ 10). In grams that’s 16.5 × 0.789 ≈ 13.0 g of ethanol — roughly 0.93 US standard drinks (13 ÷ 14). A 175 ml glass of wine at 13% ABV contains 22.75 ml ethanol → 2.275 UK units and about 17.95 g ethanol (≈1.28 US drinks).

Using the calculator for safe drinking and weight control

If you’re tracking calorie intake, include alcohol calories in your daily total. If you’re tracking units for health guidance, use the totals to plan alcohol-free days or cut down in smaller increments. The calculator makes it easy to compare options (lower ABV beers, smaller pours) and to see how small changes add up across a week.

Limitations and mixed drinks

Cocktails often contain multiple alcoholic ingredients — to be accurate, add each component’s volume and ABV or estimate based on typical recipes. Labels on craft beverages may vary, and pours at bars may be larger than assumed. Treat the calculator as a reliable estimate when you use the correct volumes and ABV values.

Responsible use and next steps

If totals show you are regularly above recommended limits, consider small changes: choose lower-ABV options, reduce serving size, alternate alcoholic with non-alcoholic drinks, or set weekly unit goals. For individuals with medical conditions, pregnancy, or medications that interact with alcohol, abstaining is the safest option. If cutting down is difficult, seek help from healthcare professionals or local support services.

Disclaimer: This calculator provides informational estimates only. For personalized health advice related to alcohol use, consult a healthcare professional.