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Peak BAC Estimate Calculator

Enter drinks, body weight, time and sex to estimate your peak BAC.

How it is calculated

The tool applies the Widmark estimate. Alcohol in grams is A = drinks × 14, since each standard drink counts as 14 g. The raw level is BACraw = A / (W × r) × 100, where W is body weight in grams (pounds × 453.592) and r is the distribution factor, 0.68 for male and 0.55 for female. The amount cleared is 0.015 × hours, in percentage points of BAC, but it is capped at the raw level because the body cannot clear more than was drunk. The headline figure is BAC = max(0, BACraw − 0.015 × hours), so it never goes below 0.000%. Weight is entered in pounds; drinks and hours can be decimals, but weight must be above zero and drinks and hours cannot be negative. Any sex value other than female is treated as male. This is a rough educational estimate, not a measurement or a driving guide.

Worked example

A man weighing 170 lb has 4 standard drinks, and 2 hours have passed. Alcohol: 4 × 14 = 56 g. Body weight: 170 × 453.592 = 77,110.6 g. Raw level: 56 / (77,110.6 × 0.68) × 100 = 56 / 52,435.2 × 100 = 0.107%. Cleared in 2 hours: 0.015 × 2 = 0.030%. Estimate: 0.107 − 0.030 = 0.077%. For a woman of the same weight, r = 0.55 gives a raw 0.132% and an estimate of 0.102%.

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Common mistakes

  • Entering weight in kilograms. The field is in pounds, so typing 77 for a 77 kg person nearly doubles the result; multiply kilograms by 2.2046 first.
  • Counting drinks, not standard drinks. One large glass of wine or a tall pour of spirits can be two standard drinks of 14 g each; the tool does not ask what the drink was.
  • Starting the clock at the last drink. Hours are counted from the first drink, since clearance runs throughout the session.
  • Reading the “metabolized” figure as alcohol that was actually present. It is 0.015 × hours but never more than the raw level, so after 10 hours the 4-drink, 170 lb example shows 0.107% (all of the raw level), not 0.150%, and the estimate is then 0.000%.
  • Treating the estimate as a safe-to-drive number. Food, medication and individual variation are not in the formula, and real levels can differ widely.

Sources

About this calculator

This calculator estimates blood alcohol concentration using the Widmark formula: BAC = (alcohol consumed in grams ÷ (body weight in grams × r)) × 100 − (β × hours elapsed), where r is the Widmark distribution factor (roughly 0.68 for men and 0.55 for women, reflecting differences in body water content) and β is the average metabolism rate of about 0.015% BAC per hour. You enter the number of standard drinks (each counted as 14 g of alcohol, so the type of drink is not asked), your weight in pounds (converted to grams at 453.592 g per lb), and the hours since the first drink; the metabolism term subtracts back out the amount your body has already processed in that time. The result is the estimate after those hours, shown next to the raw value before any elimination.

This tool is for education only, not legal or medical advice — actual BAC is affected by food intake, medications, liver function, and individual variation that the Widmark formula does not capture, and it should never be used to judge whether it's safe to drive. It's useful for understanding roughly how weight, sex, and drink pacing affect intoxication, a topic taught in health-education and responsible-drinking programs.

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Comments (1)

  • Editorial team

    For a feel of the scale: for a 170 lb man the tool puts one standard drink at about 0.027% raw, and the fixed 0.015% per hour removes that in roughly 1.8 hours. Real elimination rates vary from person to person, and the clock runs from the first drink, so treat any figure as a classroom illustration only. Does your health-education course use a different standard drink size or rate? Share it and tell us what you would compare.

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