Standard Drink Calculator

Background.

A standard drink is a counting unit, not a serving size, and the gap between the two is where almost every drink-counting error comes from. NIAAA defines the US standard drink as about 14 grams — roughly 0.6 fluid ounces — of pure alcohol, the amount in a 12 fl oz can of 5% beer, a 5 fl oz glass of 12% wine, or a 1.5 fl oz shot of 40% spirits. Nothing in that definition says anything about what a bar pours or what fits in a glass. A 16 fl oz pour of a 7% IPA is 1.87 standard drinks, and one standard drink of it would be 8.57 fl oz — barely half the glass. NIAAA makes the same point directly: a 12-ounce bottle at 10% ABV contains two standard drinks, not one.

This calculator takes the two numbers actually printed on the container — the volume and the ABV — and returns the drink count, the grams of pure ethanol, and how much of that specific beverage would make exactly one unit. It does not estimate a blood alcohol concentration, a sobering-up time, or a calorie count; those are separate pages, and keeping them separate is deliberate.

Two national definitions are implemented, and they are not the same kind of thing. The US standard drink is defined by mass: 14 grams of ethanol. The UK unit is defined by volume: 10 millilitres of ethanol, which the NHS also describes as "about 8g". Those two NHS figures are not exactly equal — 10 mL of ethanol weighs 7.89 g at the standard density of 0.789 g/mL, a difference of about 1.4% — so this page uses the volumetric form, because that is the arithmetic the NHS itself publishes. Checked against the NHS's own worked example, a 568 mL UK pint at 5.2% comes out at 2.95 units, matching its statement that "a pint of strong lager contains 3 units of alcohol". The practical consequence is that any given drink is about 1.77 times as many UK units as US standard drinks; the beer that is one US standard drink is 1.77 UK units.

Only the US and UK definitions are offered. Australia, Canada, Japan and many other countries use different masses, and their figures could not be checked against the issuing body from here — so rather than publish remembered numbers, the page states its scope and stops. The grams-of-ethanol output is definition-free, so anyone working to a different national unit can divide by their own figure.

What the number is for matters as much as what it is. Standard drinks exist so that public health guidance, screening questionnaires and research can compare a wine drinker with a whisky drinker on one scale. NIAAA uses it to define binge drinking as the amount that brings blood alcohol to 0.08% — typically four or more drinks for a woman or five or more for a man in about two hours. What the unit is not is an allowance. NIAAA's own clinical guidance states that "there is no guaranteed safe amount of alcohol for anyone", and counting drinks accurately tells you how much you have had, not whether it was safe or whether you can drive. If you are asking the driving question, the answer is a ride.

What is standard drink calculator?

Ethanol is the same molecule whatever it arrives in, so the only honest way to compare a beer with a cocktail is by how much of it each one contains. A standard drink is that comparison unit. Because ABV is a volume fraction, working out the ethanol in any drink is two steps: multiply the volume by the ABV to get the volume of pure ethanol, then multiply by ethanol's density — 0.789 g/mL, the value ANSI/ASB Best Practice Recommendation 122 §4.7 specifies for forensic alcohol calculations — to get its mass.

The unit is set by public health bodies, not by producers, and the sizes were chosen so that one unit is a plausible single serving of a typical product in that country. The US settled on 14 g, which makes an ordinary 12 oz 5% beer exactly one drink. The UK settled on 10 mL, roughly the amount an average adult metabolises in an hour, which makes a small 25 mL measure of spirits exactly one unit. Neither figure is a biological constant, and comparing a US "drink" with a UK "unit" without converting is a common way to misread international guidance by nearly a factor of two.

The reason this matters in practice is that real servings have drifted away from the reference sizes while the reference sizes stayed put. Craft beers run to 6–10% rather than 5%, wine glasses hold 8–9 oz rather than 5, and a home pour of spirits is famously generous. Every one of those drifts pushes the true count up while the drinker's mental count stays the same, and every downstream calculation — blood alcohol, weekly totals, screening scores — inherits the error. Reading the ABV off the label and measuring the pour once is the single highest-value correction available.

How to use this calculator.

1. 01Enter the volume of ONE serving and pick fluid ounces or millilitres. Use the can or bottle size, or measure the glass once.
2. 02Enter the ABV from the label. This matters more than the volume — a 7% beer is 40% more alcohol than a 5% beer in the same glass.
3. 03Set how many of that serving you are counting. Quarter-serving steps are allowed for a half glass.
4. 04Choose the definition: US standard drinks (14 g) or UK units (10 mL).
5. 05Read the drink count, and check "one unit of this drink is" — that is the pour size that would actually equal one.
6. 06Take the grams of pure alcohol across to the BAC calculator if that is the next question, or to the alcohol calories calculator for the energy content.

The formula.

The chain has three constants and each one is pinned to a primary source. The fluid-ounce conversion is exact by definition: one US gallon is 231 cubic inches and one inch is 2.54 cm, which makes one US fluid ounce 29.5735295625 mL. NIST Special Publication 811, Appendix B.9 prints 2.957 353 × 10¹ mL, agreeing to every digit it gives. Ethanol's density is 0.789 g/mL, the figure ANSI/ASB Best Practice Recommendation 122 §4.7 states for forensic alcohol calculations. The US standard drink is 14 g of ethanol, from NIAAA — and independently from ANSI/ASB 122 §4.5, which gives the same 14 g and the same three reference servings from a completely different discipline.

The strongest check on the whole chain is that all three NIAAA reference drinks have to come out at exactly one standard drink. A 12 fl oz beer at 5%, a 5 fl oz wine at 12% and a 1.5 fl oz shot at 40% each contain 17.7441 mL of ethanol, which is 14.0001 g, which is 1.00 standard drinks. If the ounce conversion, the density or the 14 g figure were wrong, at least one of those three would miss. That identity is a test on this page, not just a claim.

The US and UK branches diverge after the ethanol volume is known. For the US, multiply by density to get grams and divide by 14. For the UK, divide the millilitres by 10 and skip density entirely — which is why the UK branch cannot inherit an error from the density constant at all. Because 14 g of ethanol occupies 17.744 mL and a UK unit is 10 mL, any drink is 1.774 times as many UK units as US standard drinks, whatever it is. The default 12 fl oz 5% beer is 1.00 US standard drinks and 1.77 UK units; the 16 fl oz 7% IPA is 1.87 and 3.31.

The "one unit of this drink is" figure runs the calculation backwards. One US standard drink is 14 ÷ 0.789 = 17.744 mL of ethanol; dividing by the ABV fraction scales that up to the beverage volume that carries it. Because ABV sits in the denominator, stronger drinks need less volume: 12.00 fl oz at 5%, 8.57 fl oz at 7%, and 1.50 fl oz at 40%. Those last two are worth sitting with — a shot glass and a pint glass can hold the same amount of alcohol. This is also why the calculator refuses an ABV of zero: with no alcohol there is no volume of the drink that equals one unit, and returning infinity would be worse than an error message.

Rounding happens exactly once. Every intermediate quantity is carried at full precision and only the displayed outputs are rounded, to two decimal places, half up. Two decimals is the right precision for a drink count — 1.87 standard drinks is a meaningful statement and 1.8667 is false precision about a pour nobody measured to the microlitre. Because there is a single terminal rounding step and no classification thresholds on this page, the boundary behaviour is simple: a true value of 17.745 mL prints 17.75 and 17.744 prints 17.74, which is asserted directly in the tests.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Institute on Alcohol Abuse and Alcoholism (updated December 2025). "What Is A Standard Drink?" — "In the United States, one standard drink contains about 14 grams, or about 0.6 fluid ounces, of pure alcohol", with the seven reference servings reproduced on this page.
2. [2]NHS (United Kingdom). "Alcohol units." — "One unit equals 10ml or 8g of pure alcohol"; "a pint of strong lager contains 3 units of alcohol", the worked example this calculator is checked against.
3. [3]AAFS Academy Standards Board (2024). ANSI/ASB Best Practice Recommendation 122, 1st Ed., "Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology." §4.5 (standard drink ≈ 14 g, with the same three reference servings) and §4.7 ("The density of alcohol is 0.789 g/mL").
4. [4]National Institute of Standards and Technology. NIST Special Publication 811, "Guide for the Use of the International System of Units (SI)", Appendix B.9 — ounce (U.S. fluid) → millilitre, 2.957 353 E+01.
5. [5]National Institute on Alcohol Abuse and Alcoholism. Core Resource on Alcohol — "The Basics: Defining How Much Alcohol Is Too Much." Source of the binge-drinking definition (BAC 0.08%, typically 4+ drinks for women or 5+ for men in about two hours) and of "there is no guaranteed safe amount of alcohol for anyone".