Blood Alcohol Content (BAC) Calculator
Enter your sex, weight, number of drinks and time spent drinking to estimate your blood alcohol content (BAC).
Reviewed by the ToolNestr Editorial Team — July 2026
Enter your details to estimate your BAC.
This is an educational estimate only. Never drink and drive. If you plan to drink, arrange a safe ride home.
About blood alcohol content
Blood Alcohol Content (BAC) measures the concentration of alcohol in your blood. It is used legally to determine impairment for driving and other activities. This calculator uses the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s, which remains the standard method for estimating BAC. BAC is influenced by many factors beyond those in the formula — your food intake, hydration, liver health, genetics, medications and fatigue all affect your actual BAC. This is not a medical or legal instrument. If you plan to drink, arrange a safe ride home in advance. See also the Calorie Calculator for the calorie content of alcohol.
How it works
The Widmark formula estimates peak BAC using the number of standard drinks, body weight, sex (which affects the distribution ratio) and time elapsed. One standard drink contains ~14 g of pure alcohol in the US (12 oz beer, 5 oz wine, 1.5 oz spirits). The formula calculates total alcohol consumed, divides by body water volume (adjusted for sex), then subtracts the alcohol metabolised during the drinking period. The metabolism rate is approximately 0.015% BAC per hour, though this varies.
The formula explained
Widmark formula: BAC = ((drinks × 14 g × 100) / (weight (g) × r)) − (metabolism × hours)
Where r (distribution ratio): Men = 0.68, Women = 0.55
Metabolism: ~0.015 g/100mL/hour
Worked example
A 75 kg man drinks 4 standard beers over 3 hours. What is his estimated BAC?
Social drinker
Plan your evening by understanding how many drinks you can have before reaching impairing levels. Always arrange a safe ride home.
Designated driver
Understand how long it takes for alcohol to leave your system after a night out. The only safe level for driving is 0.00%.
Health educator
Use the calculator to teach students about alcohol metabolism, impairment levels and why coffee and cold showers do not speed up sobriety.
College student
Learn about BAC and make informed decisions about drinking. Know your limits and understand that impairment starts well below the legal limit.
How to use this calculator
Enter your details
Provide your sex and weight. The Widmark formula uses different distribution ratios for men and women.
Log your drinks and time
Enter the number of standard drinks and the total hours you have been drinking. Time matters — spreading drinks out lowers peak BAC.
Read your estimate
See your estimated BAC, whether it is above the legal limit, and how long until it reaches zero. Plan accordingly and never drink and drive.
Important safety information
Only time lowers BAC
Coffee, cold showers, vomiting, exercise or fresh air do not speed up alcohol metabolism. Only your liver processing alcohol over time reduces your BAC. The average rate is 0.015% per hour.
Impairment starts below the legal limit
At 0.02–0.04% BAC, most people experience reduced judgement and coordination. At 0.05–0.07%, impairment is significant. Do not drive after any amount of alcohol.
Standard drink sizes vary
A standard drink in the US is 14 g of alcohol (12 oz beer at 5%, 5 oz wine at 12%, 1.5 oz spirits at 40%). Many restaurant and home pours are larger — account for this when estimating your intake.
Related tools
Frequently asked questions
What is BAC?
Blood Alcohol Content (BAC) is the percentage of alcohol in your bloodstream. A BAC of 0.08% means 0.08 g of alcohol per 100 mL of blood, which is the legal driving limit in most US states.
How accurate is the Widmark formula?
The Widmark formula provides a reasonable estimate but individual factors — metabolism, liver function, food consumed, hydration and genetics — cause significant variation. Use it as an educational tool, not a precise measurement.
How quickly does the body metabolise alcohol?
The liver processes alcohol at an average rate of about 0.015–0.020% BAC per hour, or roughly one standard drink per hour. Nothing speeds this up — not coffee, cold showers or exercise.
What factors affect BAC?
Weight (more body water dilutes alcohol), sex (women generally have less body water and lower alcohol dehydrogenase activity), food (slows absorption), carbonation (speeds absorption), and genetics all influence BAC.
What is the legal BAC limit?
In most US states, the legal driving limit is 0.08% for drivers aged 21+. For commercial drivers it is 0.04%. Many countries have lower limits (0.05% in most of Europe, 0.02% in some).