Widmark formula · Every legal limit · Honest error bars
BAC Calculator
Estimate your blood alcohol content from weight, drinks, and time, with the honesty most calculators skip: this is education, not permission to drive.
Beer
12 oz at 5% · 1.0 std
Light beer
12 oz at 4.2% · 0.8 std
Craft beer / IPA
16 oz at 6.7% · 1.8 std
Hard seltzer
12 oz at 5% · 1.0 std
Glass of wine
5 oz at 12% · 1.0 std
Large wine pour
8 oz at 13% · 1.7 std
Shot of spirits
1.5 oz at 40% · 1.0 std
Cocktail
~2 oz of 40% spirits · 1.3 std
Tap + to add drinks. 1 standard drink = 14g of alcohol.
Enter your weight, add your drinks, and set the hours since your first drink for a live estimate with a burn-off timeline. Educational only, never a green light to drive.
This is an estimate only. No calculator, app, or rule of thumb can tell you it is safe to drive. If you have been drinking, do not drive: arrange a ride, call a cab, or stay put. Impairment starts below every legal limit.
How the Widmark formula works
Every serious BAC calculator, including breath-test cross-checks used in court, starts from the same 1930s physiology worked out by Erik Widmark. Alcohol distributes through your body water, so peak BAC is the alcohol you drank divided by the water available to dilute it, then your liver subtracts a steady 0.015% per hour:
BAC% = (grams of alcohol / (weight in grams x r)) x 100 minus (0.015 x hours)
The distribution ratio r is about 0.68 for men and 0.55 for women, reflecting average body-water differences. One US standard drink is 14 grams of pure alcohol.
Worked example: an 80kg man has 4 standard drinks over 2 hours. That is 56g of alcohol into 80,000g x 0.68 of distribution, a peak of about 0.103%. Subtract 2 hours of elimination (0.030%) and his estimated BAC is 0.073%: under 0.08%, over 0.05%, and measurably impaired either way.
The formula's honest weakness: it assumes average physiology and fully absorbed alcohol. Food in your stomach, medications, fatigue, and heavy pours can move the real number by 0.02% or more in either direction, which is why we show bands and burn-off curves instead of pretending three decimal places of certainty.
How long until you are actually sober
Your liver clears roughly one standard drink per hour and takes no requests: coffee, showers, and food after the fact change how awake you feel, not your BAC. From 0.08% you are five to six hours from zero; after a heavy night you can still be over the limit at breakfast. The calculator above projects your personal curve, and the guides below cover the detail.
Alcohol in your system →
Blood, breath, urine, and hair detection windows.
Legal limits, everywhere →
Every US state, plus AU, UK, EU and beyond.
How long until sober? →
The 0.015%/hour math, from any starting point.