A "standard drink" in the United States is not a measurement of how much liquid is in your glass — it is a measurement of how much pure alcohol that glass contains. The National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines one US standard drink as any beverage that contains about 0.6 fluid ounces (roughly 14 grams) of pure ethanol. That sounds simple, but the real world is confusing: a 12-oz beer, a 5-oz glass of wine, and a 1.5-oz shot of spirits all look very different in size, yet they each count as roughly one standard drink — when they are at typical strengths. Pour your own wine a little heavier, order a double, or choose an 8% craft beer, and suddenly your "two drinks" are actually four.
This standard drink calculator converts any combination of volume and ABV into a clean count of US standard drinks, then uses the Widmark formula to estimate your blood alcohol concentration (BAC) and the extra hours you need before your body clears that alcohol. It is deliberately built on the US 0.6-ounce definition, which is different from the UK "alcohol unit" system (where one unit is 10 ml of pure alcohol). If you have ever wondered exactly how much alcohol you actually drank, this is the tool.
How to Use
- Enter the Volume per Drink in US fluid ounces. A standard bottle or can of beer is about 12 oz; a typical restaurant pour of wine is 5 oz; a shot of spirits is 1.5 oz.
- Set the ABV (Strength) as a percentage printed on the label. Ordinary beer is usually 4–7%, table wine is 12–14%, and most spirits are about 40%.
- Type the Number of Drinks you consumed. This lets the calculator scale a single pour up to a whole evening.
- Add your Body Weight in pounds and your Biological Sex. These set the Widmark distribution constant — 0.73 for male bodies and 0.66 for female bodies — because women and men of the same weight distribute alcohol through body water differently.
- Enter the Hours Since First Drink. Alcohol metabolizes at a rough average of 0.015% BAC per hour, so elapsed time lowers your estimate.
- Read the result card: Pure Alcohol in grams, US Standard Drinks, your Estimated BAC, and the Additional Hours to Sober.
The engine first works out the pure alcohol: multiply volume by ABV (converted from a percent to a fraction) and by the number of drinks. It then divides that pure-alcohol volume by 0.6 oz to get the standard-drink count. From the same pure-alcohol amount it runs the Widmark equation, subtracts the hourly metabolism, and reports how many more hours you need to reach a BAC near zero.
The US Standard Drink Definition
The 0.6-ounce rule exists so people can compare drinks that come in wildly different containers:
- Beer (12 oz at 5% ABV): 12 × 0.05 = 0.6 oz pure alcohol → 1 standard drink.
- Table wine (5 oz at 12% ABV): 5 × 0.12 = 0.6 oz → 1 standard drink.
- Spirits / shot (1.5 oz at 40% ABV): 1.5 × 0.40 = 0.6 oz → 1 standard drink.
The catch is that real servings rarely match those textbook sizes. A "tall" 16-oz draft at 6.5% ABV is (16 × 0.065) / 0.6 = 1.73 standard drinks, not one. A generous 8-oz wine pour at 14% is (8 × 0.14) / 0.6 = 1.87 standard drinks. This is why people consistently underestimate their intake: the glass looks like "one drink," but the math says otherwise.
How BAC Is Estimated (Widmark Formula)
Once the calculator knows your pure alcohol, it applies the classic Widmark forensic formula used in toxicology and by NHTSA:
BAC = pureAlcoholOz × 5.14 / (weightLbs × r) − 0.015 × hours
Where r is the gender distribution constant (0.73 male, 0.66 female), and 0.015 is the average hourly drop in BAC as the liver metabolizes alcohol. The number 5.14 is the conversion constant that folds in the density of ethanol and unit conversions for the US system. Because individual metabolism, food, medications, and hydration vary widely, the result is an estimate — never a breathalyzer reading.
Examples
Example 1 — A regular beer. A 180-lb man drinks one 12-oz beer at 5% ABV and waits one hour. Pure alcohol is 12 × 0.05 = 0.6 oz (about 14 grams), which is 1.0 standard drink. His estimated BAC works out to about 0.0085%, and he needs roughly 0.56 additional hours to clear it. This is well under the 0.08% legal driving limit.
Example 2 — Two glasses of wine. A 140-lb woman has two 5-oz pours of 12% wine over two hours. Pure alcohol is 2 × 5 × 0.12 = 1.2 oz, or 2.0 standard drinks. Her estimated BAC is about 0.0368%, with around 2.45 more hours needed to fully sober. Because the female Widmark constant is lower, she reaches a higher BAC than a man of the same weight drinking the same amount.
Example 3 — A heavy craft beer. A 190-lb man drinks a single 19-oz double IPA at 8.0% ABV. Pure alcohol is 19 × 0.08 = 1.52 oz, which is (1.52 / 0.6) = 2.53 standard drinks from just one can. The calculator immediately shows that one large craft beer equals two and a half standard drinks — a common surprise.
FAQ
What counts as one US standard drink?
One US standard drink contains about 0.6 fluid ounces (14 grams) of pure alcohol. In practice that is a 12-oz beer at 5% ABV, a 5-oz glass of wine at 12%, or a 1.5-oz shot of 40% spirits. Larger pours or higher ABV mean more than one standard drink.
How is the number of standard drinks calculated?
Multiply the drink volume in ounces by the ABV as a decimal, then multiply by the number of drinks, and finally divide by 0.6. For example, 12 oz × 0.05 × 1 ÷ 0.6 = 1.0 standard drink. This is the NIAAA definition used across the United States.
How is this different from UK alcohol units?
The US standard drink is based on 0.6 fl oz (about 14 g) of pure alcohol, while the UK unit is based on 10 ml (about 8 g). So one US standard drink is roughly 1.5 UK units. This calculator uses the US 0.6-ounce standard; for UK units and the 14-unit weekly NHS guideline, use a dedicated UK unit calculator.
How accurate is the estimated BAC?
The Widmark formula gives a reasonable ballpark but is not a breathalyzer. Actual BAC depends on your metabolism, how much food is in your stomach, medications, hydration, body composition, and genetics. Treat the result as an order-of-magnitude estimate, not a precise reading.
How many hours does it take to sober up?
The liver metabolizes alcohol at roughly 0.015% BAC per hour on average. This calculator divides your estimated BAC by 0.015 to show the additional hours needed. Coffee, cold showers, and exercise do not speed this up — only time does.
How many standard drinks are safe?
US dietary guidelines advise up to 1 drink per day for women and 2 for men, and many public-health experts recommend even less. "Safe" varies by individual, pregnancy status, medications, and liver health. This tool counts drinks; it does not clear you to drive or operate machinery.
Disclaimer
This standard drink calculator is provided for informational purposes only and is not medical advice. Estimated BAC and hours-to-sober figures are approximations based on the Widmark formula and average metabolism; they are not a substitute for a breathalyzer, a doctor's assessment, or clinical care. Do not rely on these estimates to decide whether it is safe to drive. Never drink and drive — if you have been drinking, use a designated driver, taxi, or rideshare. Pregnant people, people on medication, and people with liver disease should avoid alcohol entirely and consult a qualified healthcare professional.