How do I calculate how many standard drinks are in any beverage?

Multiply volume (ml) × ABV (as a decimal) × 0.789 to get grams of pure alcohol, then divide by your country's standard (14 g in the US). Example: a 473 ml pint of 8% IPA = 473 × 0.08 × 0.789 ≈ 30 g ≈ just over 2 US standard drinks.

Why do standard drink definitions differ by country?

The definitions are public-health conventions, not physical constants. The UK defines one unit as 8 g of pure alcohol, Australia uses 10 g, and the US uses 14 g. The same glass of wine therefore counts as a different number of drinks depending on the country's standard.

← Back to Home

What Is a Standard Drink?

Q: Is a cocktail one standard drink?

Usually not. A classic margarita or martini typically contains 1.5-2+ US standard drinks, and stronger cocktails like a Long Island Iced Tea can contain 2-4. Recipes and bartender pours vary widely, which makes cocktails one of the biggest sources of undercounting.

Q: Does one standard drink equal a specific BAC?

No. The estimated BAC from one standard drink depends on body weight, body composition, biological sex, food intake, and timing. Pharmacokinetic models like the Widmark formula can estimate it for a specific person, but the result is an educational approximation with roughly ±20% variance — never a basis for decisions about driving.

Sizes, the ABV math, how definitions differ by country — and why "I had three drinks" is less precise than it sounds.

Last updated: July 3, 2026

The US definition

In the United States, one standard drink contains about 14 grams (0.6 fl oz) of pure alcohol. That is roughly:

12 oz (355 ml) of beer at 5% ABV
5 oz (148 ml) of wine at 12% ABV
1.5 oz (44 ml) of spirits at 40% ABV

The point of the convention: those three very different-looking servings deliver approximately the same alcohol. Your body doesn't care whether the 14 grams arrived as beer or bourbon.

The math for any drink

Pure alcohol doesn't come labeled in grams, but it is easy to compute from the label:

grams of alcohol = volume (ml) × ABV (decimal) × 0.789

(0.789 g/ml is the density of ethanol.) Two examples:

A 473 ml (16 oz) pint of 8% craft IPA: 473 × 0.08 × 0.789 ≈ 30 g ≈ 2.1 US standard drinks — one pint, two drinks
A generous 200 ml restaurant pour of 14% red wine: 200 × 0.14 × 0.789 ≈ 22 g ≈ 1.6 standard drinks

This is why casual counting drifts: modern craft beers, large wine pours, and cocktails all routinely exceed one standard drink per glass.

Country differences

"Standard drink" is a public-health convention, and countries define it differently:

Country	Grams of pure alcohol per standard drink/unit
United Kingdom (1 unit)	8 g
Australia	10 g
Canada	≈ 13.5 g
United States	14 g
Japan (1 go-based unit)	≈ 20 g

The same 5 oz glass of wine is therefore "one drink" in the US but about 1.7 units in the UK. When reading guidance from another country, check which definition it uses.

Cocktails: the big undercount

Cocktails are where drink counting fails most often. A classic margarita or martini typically contains 1.5–2+ US standard drinks; a Long Island Iced Tea can contain 2–4. Recipes vary, bartenders pour differently, and the mixer volume hides the alcohol. Logging a cocktail as "one drink" can understate actual alcohol by half or more — which then flows directly into any BAC estimate's error.

How SipLogger uses this

SipLogger ships with 40+ drink templates — beers, wines, spirits, and cocktails — each pre-configured with realistic volume and ABV, so a logged drink carries its actual estimated alcohol content into the Widmark-based calculation rather than a vague "one drink" unit. For anything unusual, you can create custom drinks with any volume and ABV. Better inputs make the educational estimate more meaningful — though it always remains an estimate with roughly ±20% variance, never a measurement.

Frequently Asked Questions

How do I calculate standard drinks in any beverage?

Multiply volume (ml) × ABV (decimal) × 0.789 to get grams of pure alcohol, then divide by your country's standard (14 g in the US). A 473 ml pint of 8% IPA works out to about 30 g — just over 2 US standard drinks.

Is a cocktail one standard drink?

Usually not. A margarita or martini is typically 1.5–2+ US standard drinks; a Long Island Iced Tea can be 2–4. Recipes and pours vary widely, making cocktails the most commonly undercounted drink.

Why do definitions differ by country?

They are public-health conventions, not physical constants. The UK unit is 8 g, Australia's standard drink is 10 g, the US uses 14 g. The same glass counts differently depending on whose standard you apply.

Does one standard drink equal a specific BAC?

No. The estimated BAC from one drink depends on body weight, composition, biological sex, food, and timing. Models like the Widmark formula can estimate it for a specific person — as an educational approximation with roughly ±20% variance, never a basis for driving decisions.