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Drinks to Reach BAC Calculator

Estimate the standard drinks needed to hit a target BAC by sex and body weight.

How it is calculated

The tool runs the Widmark formula backwards to find the alcohol needed to reach a target blood alcohol level:

alcohol (g) = (BAC / 100) × weight (kg) × 1000 × r

drinks = alcohol (g) / 14

BAC is entered in percent (0.08 means 0.08 %), weight in kilograms, and r is the Widmark distribution ratio: 0.68 for male and 0.55 for female. One standard drink is taken as 14 g of pure alcohol, the US definition; other countries use other sizes. The result is a number of drinks with two decimals. The formula has no time term, so it assumes everything is absorbed at once and nothing is yet metabolised. It is a rough estimate for awareness, not a way to judge fitness to drive.

Worked example

A male weighing 70 kg, target BAC 0.08.

Alcohol = (0.08 / 100) × 70 × 1000 × 0.68 = 0.0008 × 70,000 × 0.68 = 38.08 g.

Drinks = 38.08 / 14 = 2.72, so the tool shows 2.72 standard drinks.

With the female ratio of 0.55 the same weight and target would need fewer drinks, because the alcohol is spread through less body water.

Try this example →

Common mistakes

  • Typing the target as a percentage of 8 instead of 0.08. The field is in percent, so 8 returns 272 drinks, a level that no one survives.
  • Entering body weight in pounds. The formula multiplies by 1000 to get grams from kilograms, so pounds overstate the weight and the number of drinks.
  • Treating the result as drinks over an evening. There is no time or metabolism in the formula, so it describes peak BAC if all the alcohol were absorbed at once.
  • Counting a large pour, a strong beer or a cocktail as one drink. The tool counts 14 g of pure alcohol per drink, and many servings hold more than that.
  • Using the result to decide whether it is safe to drive. Food, medication, drinking speed and individual differences move real BAC well away from this estimate.

Sources

About this calculator

Blood alcohol concentration (BAC) from a given number of drinks is commonly estimated with the Widmark formula, which accounts for the alcohol content and volume of standard drinks, body weight, and a sex-based distribution ratio (alcohol disperses through total body water, which differs by sex and body composition). In practice the liver also clears alcohol steadily over time, which this calculation does not include. Running the formula in reverse — solving for drinks instead of BAC — tells you roughly how many standard drinks it takes to reach a chosen BAC level.

This kind of estimate is used in harm-reduction teaching to show how few drinks it takes to reach a given level, though individual variation in metabolism, food intake, and drinking rate means any BAC estimate is approximate and should never be relied on to decide it's safe to drive.

Working back from a target BAC in percent (0.08, for example), your sex and weight in kilograms, it estimates how many standard drinks of 14 g pure alcohol would produce that level if all of it were in your body at once; time and metabolism are not counted.

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