Blood Alcohol (BAC) Calculator

Estimate your blood alcohol content

This BAC calculator gives a rough estimate of blood alcohol content (BAC) from your drinks, body weight, sex and the time since you started drinking. It uses the Widmark formula. The result is an estimate for general information only. It can be far from your real BAC, and it must never be used to decide whether you are safe to drive. If you have been drinking, do not drive.

How to use it

1. Choose a Drink Type: beer (12 oz, 5%), wine (5 oz, 12%), shot (1.5 oz, 40%) or cocktail (8 oz, 10%).
2. Enter the Number of Drinks.
3. Enter Hours Since Drinking Started.
4. Enter your Body Weight in pounds and choose Gender.
5. Read the estimated BAC, the effects note and the estimated hours until sober.

How it works

The calculator uses the Widmark formula:

BAC % = alcohol grams ÷ (body weight in grams × r) × 100 − 0.015 × hours

• Alcohol grams = drinks × drink size in oz × 29.5735 ml × ABV × 0.789 g/ml (the density of alcohol).
• Body weight in pounds is multiplied by 453.592 to get grams.
• r (body water ratio) is 0.73 for male and 0.66 for female.
• The body is assumed to remove 0.015% BAC per hour. The result never goes below 0.

Estimated hours until sober = BAC ÷ 0.015. For example, 3 beers, 160 lb, male, 2 hours gives about 0.049%.

What the result shows

The BAC is shown with three decimals. At 0.08% or more, the tool notes that this is over the US legal driving limit. Many countries set a lower limit, and some have a zero limit. The effects note is a general description by BAC range, not a measure of how you feel.

Why it is only an estimate

Real BAC depends on food, the pace of drinking, health, medicine and how your own body handles alcohol. The tool uses one drink type at a time and fixed drink sizes, so mixed or larger drinks are not counted exactly.

Frequently asked questions

Can I use this to know if I can drive?

No. This is a rough estimate and can be wrong by a large margin. Even a low BAC can affect driving. If you have been drinking, do not drive. Use a taxi, public transport or a sober driver.

What formula does the BAC calculator use?

It uses the Widmark formula with r = 0.73 for males and 0.66 for females, and subtracts 0.015% for each hour since drinking started.

Is my information stored?

No. The estimate is worked out in your browser. Nothing you enter is saved or sent anywhere.