Alcohol Consumed — Ethanol Enters the Stomach
A measured dose of ethanol enters the gut for absorption.
- 14 g: Standard US Drink (Pure ethanol content in one standard drink.)
- 14 g: Beer, 12 oz at 5% (Matches a shot of liquor in ethanol.)
- 14 g: Wine, 5 oz at 12% (Standardized so drink types compare fairly.)
- ~10 min: Absorption Start (Stomach lining begins absorbing ethanol quickly.)
Stomach absorption
Ethanol crosses the stomach lining almost immediately after swallowing.
Small intestine uptake
Most alcohol absorbs faster once it reaches the small intestine.
Food slows absorption
A full stomach delays how quickly BAC rises.
Distribution Into Total Body Water
Ethanol disperses evenly through the body's water volume.
- ~60%: Total Body Water, Male (Roughly three-fifths of male body mass.)
- ~50%: Total Body Water, Female (Lower water fraction than typical males.)
- 0.68: Distribution Ratio r, Male (Fraction of body weight ethanol reaches.)
- 0.55: Distribution Ratio r, Female (Reflects higher body fat, less water.)
Water-soluble ethanol
Ethanol dissolves freely into blood plasma and tissue water.
Fat tissue excluded
Fat holds little alcohol, concentrating it in lean tissue.
Sex and body composition
Body composition changes exactly how far ethanol spreads.
The Widmark Formula — Calculating BAC
A simple equation converts grams of alcohol into blood concentration.
- A / (r·W): Formula (Grams divided by weight times ratio.)
- 1932: Published (Erik Widmark first formalized the calculation.)
- % w/v: Result Units (Grams alcohol per 100 milliliters of blood.)
- Today: Still In Use (Courts and researchers still rely on it.)
Grams of alcohol, A
Total ethanol consumed drives the entire calculation.
Body weight, W
Heavier bodies dilute the exact same dose of alcohol.
Distribution ratio, r
The ratio scales alcohol to the total body water share.
Peak BAC — Absorption Completes
Blood alcohol concentration reaches its highest point after absorption.
- 30–90 min: Typical Peak Timing (Peak usually arrives within about an hour.)
- 0.08%: US Legal Driving Limit (Standard threshold across most US states.)
- 0.02%: Impairment Onset (Noticeable effects begin at low concentrations.)
- 0.30%+: Severe Risk Zone (Risk of losing consciousness rises sharply.)
Absorption plateau
Alcohol entering the blood equals alcohol leaving it briefly.
Peak timing varies
Food, drink speed, and metabolism all shift the timing.
Legal threshold reference
Peak BAC is measured directly against legal driving limits.
Elimination — BAC Declines Over Time
The liver clears alcohol at a steady, mostly fixed rate.
- 0.015%/hr: Elimination Rate, β (Average BAC decline for each passing hour.)
- Zero-order: Kinetics Type (Rate stays constant regardless of concentration.)
- ~5.3 hr: Time To Sober, 0.08% (Hours needed to clear a moderate peak.)
- ~1 drink/hr: Liver Capacity (Roughly one standard drink metabolized hourly.)
Zero-order elimination
Alcohol clears at a constant rate, not an exponential one.
Alcohol dehydrogenase
Liver enzymes steadily oxidize ethanol into acetaldehyde.
No real shortcuts
Coffee and cold showers do not speed elimination.