What this calculator does
A US standard drink is defined as 14 grams of pure alcohol, and the familiar serving sizes were chosen to match it. That is why a 355 mL beer at 5 per cent, a 148 mL glass of 12 per cent wine and a 44 mL shot of 40 per cent spirit all come out at almost exactly one drink.
The equivalence breaks as soon as the serving changes. A UK pint of 4.5 per cent beer is 1.44 standard drinks, and a generously poured glass of wine can easily be two.
The formula
Volume is multiplied by the alcohol fraction and by the density of ethanol, 0.789 g/mL, to give grams of pure alcohol. Dividing by 14 gives the number of standard drinks.
| Term | Meaning |
|---|---|
| Standard drink | 14 grams, or 0.6 fluid ounces, of pure alcohol under the US definition. |
| ABV | Alcohol by volume, the strength printed on the label. |
| Ethanol density | 0.789 g/mL, which converts volume of alcohol into mass. |
The inputs explained
| Field | What to enter |
|---|---|
| Drink volume (mL) | Drink volume in millilitres. A US beer can is 355 mL and a shot 44 mL. |
| Alcohol by volume (%) | Alcohol by volume as a percentage. |
When to use it
Counting drinks accurately
Guidance is written in standard drinks, so actual servings need converting.
Comparing beer, wine and spirits
The standard servings are equivalent; anything else is not.
Understanding a poured drink
Home pours are commonly much larger than a standard serving.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Why are the standard servings all one drink?
Different volumes and strengths compared on the same scale.
| Volume at 5% ABV | US standard drinks | Pure alcohol content |
|---|---|---|
| 150 mL | 0.42 | 5.9 g |
| 355 mL | 1.00 | 14.0 g |
| 500 mL | 1.41 | 19.7 g |
| 568 mL | 1.60 | 22.4 g |
Questions
Why do standard drinks differ between countries?
Because each country picked its own figure. The US uses 14 grams, the UK unit is 8 grams, Australia uses 10 and Japan about 20. Counts are not transferable, which makes international guidance easy to misread.
Where does 0.789 come from?
It is the density of ethanol in grams per millilitre. ABV gives the volume of alcohol in a drink, and multiplying by density converts that volume into the mass the standard is defined by.
Is a home pour a standard drink?
Usually not. Studies of free pouring consistently find people pour considerably more than a standard serving, particularly with wine and spirits and particularly into larger glasses.
Does the type of drink matter?
Not for the alcohol itself. A standard drink of beer, wine and spirits delivers the same 14 grams. What differs is how quickly it tends to be consumed and what else comes with it.
For the UK equivalent, see the UK alcohol units calculator. For a blood alcohol estimate, see the blood alcohol content calculator.