How to Calculate Grams of Pure Alcohol in Any Drink
The formula is simple: Volume (ml) × ABV × 0.789 = grams of ethanol. A 330ml beer at 5% = 13g. Use the calculator below to turn those grams into your exact BAC.
Calculate Your BAC from Grams →Whether you are tracking your intake for health reasons, calculating BAC before driving, or simply curious about what is in your glass, knowing the grams of pure ethanol in a drink is the foundation of all alcohol math. The formula is simple, universal, and works for every drink on the planet.
The Formula Explained: Volume × ABV × 0.789
The grams of pure ethanol in any drink is calculated as:
Grams of ethanol = Volume (ml) × ABV (as decimal) × 0.789
- Volume (ml): The total liquid volume of the drink in millilitres.
- ABV (decimal): Alcohol by volume as a decimal — so 5% = 0.05, 40% = 0.40.
- 0.789: The density of pure ethanol in g/ml at 20°C (68°F). See our full explainer on why 0.789 is the key constant.
The multiplication of Volume × ABV gives you the millilitres of pure ethanol. Multiplying by 0.789 converts those millilitres into grams, which is what the Widmark BAC formula requires.
Why 0.789 Is the Density Constant
Pure ethanol (C₂H₅OH) has a density of 0.789 grams per millilitre at 20°C. This is a physical property of the molecule — ethanol is less dense than water (1.0 g/ml). ABV labels are legally required to be measured at 20°C, which is why 0.789 is the internationally standardised constant. See our dedicated article on ethanol density for the full physics explanation, including how density shifts slightly with temperature.
Worked Examples for Beer, Wine, and Spirits
Standard European Beer (330ml, 5% ABV)
330 ml × 0.05 × 0.789 = 13.0 grams of ethanol. This is the most common calculation reference point. See the detailed breakdown in our article on 330ml beer ethanol grams.
Standard Wine Glass (175ml, 13% ABV)
175 ml × 0.13 × 0.789 = 18.0 grams of ethanol. A 175ml pour is the standard pub measure in the UK. See our full breakdown for 175ml wine grams by ABV.
UK Pub Shot (25ml, 40% ABV)
25 ml × 0.40 × 0.789 = 7.9 grams of ethanol. This is a single UK pub measure. The US shot is 44ml (1.5oz), giving 13.9g at 40% ABV.
| Drink | Volume | ABV | ml Ethanol | Grams Ethanol | US Std Drinks |
|---|---|---|---|---|---|
| 330ml lager | 330ml | 5% | 16.5ml | 13.0g | 0.93 |
| 500ml lager | 500ml | 5% | 25.0ml | 19.7g | 1.41 |
| 175ml wine | 175ml | 13% | 22.75ml | 18.0g | 1.28 |
| 250ml wine | 250ml | 13% | 32.5ml | 25.6g | 1.83 |
| UK shot (25ml) | 25ml | 40% | 10.0ml | 7.9g | 0.56 |
| US shot (44ml) | 44ml | 40% | 17.6ml | 13.9g | 0.99 |
| 568ml pint (4%) | 568ml | 4% | 22.7ml | 17.9g | 1.28 |
Grams = Volume × ABV × 0.789. US standard drink = 14g.
Now that you know the grams in your drink, enter them into the BAC calculator to see your estimated blood alcohol level.
Calculate Your BAC from Grams →What Grams of Alcohol Actually Mean for Your BAC
The Widmark formula uses grams of alcohol directly: BAC = (grams alcohol) ÷ (body weight in grams × r factor) × 100. For a 70kg man with r = 0.68, each 13g beer raises BAC by approximately 0.027%. Understanding grams lets you translate any drink into a BAC prediction, regardless of whether it is a craft beer, a cocktail, or an unusual spirit.
Standard Drink Definitions and Grams of Alcohol
Different countries define a "standard drink" differently, which creates enormous confusion. Here is a comparison:
| Country | Standard Drink | Grams of Alcohol |
|---|---|---|
| United States | 1 standard drink | 14g |
| United Kingdom | 1 unit | 8g |
| Poland | 1 standard drink | 10g |
| Australia | 1 standard drink | 10g |
| Germany | 1 Einheit | 12g |
| France | 1 verre | 10g |
| Canada | 1 standard drink | 13.45g |
| Japan | 1 unit | 19.75g |
This variation means a label saying "1.5 standard drinks" in Australia means something very different than the same label in the US. Always calculate using grams for consistent BAC math. Read our full comparison in standard drink sizes worldwide.
Want to see what the grams in your drink do to your BAC over time? The calculator handles all the Widmark math for you.
Try the Alcomato BAC Calculator →Frequently Asked Questions
Does the type of drink affect how grams are calculated?
No. The formula Volume × ABV × 0.789 works for every alcoholic drink — beer, wine, spirits, cocktails, hard seltzer, cider. The only variables are volume and ABV. The type of drink does not change ethanol density.
Why do UK units use grams differently than US standard drinks?
The UK unit (8g) was originally defined as roughly the amount of alcohol a healthy liver can process in one hour. The US standard drink (14g) was set by health authorities for dietary guidelines tracking. Neither is "correct" — they serve different purposes. Always specify which system you are using when discussing drink counts.
Can I use oz instead of ml?
Yes, with a conversion. 1 fl oz = 29.5735ml. So a 12 fl oz drink = 354.9ml. Then apply the same formula: 354.9 × ABV × 0.789 = grams of ethanol. Alternatively, there is a simplified US formula: fl oz × ABV × 23.37 = grams.
Ready to calculate your BAC from any drink? Enter your drinks and get your estimated blood alcohol level instantly.
Calculate Your BAC Now →Disclaimer: This article provides educational information only. It does not constitute medical or legal advice. BAC calculators provide estimates, not exact measurements. Individual BAC varies based on numerous factors including body composition, metabolism, food intake, medications, and health conditions. Never rely solely on calculators to determine if you are safe to drive. The only safe BAC for driving is 0.00%. Always use alternative transportation after consuming alcohol. If you struggle with alcohol use, consult a healthcare professional or contact SAMHSA's National Helpline at 1-800-662-4357.