BAC Calculator
Estimate blood alcohol content over time using the Widmark formula.
Inputs
Sex affects the Widmark distribution constant (r).
1 US standard drink = 0.6 fl oz (14 g) of pure alcohol.
Used to calculate when BAC returns to zero.
BAC now
0.0521%
Peak BAC
0.0746%
Hours until sober
4.97
Legal status
Moderate — below US legal limit (0.08 %)
Step by step
Widmark constant (r)
= 0.73 (male)
Pure alcohol
3 drinks × 0.6 oz
= 1.80 oz
Peak BAC
(1.80 × 5.14) / (170.0 × 0.73)
= 0.0746 %
BAC after elimination
0.0746 − 0.015 × 1.5 hrs
= 0.0521 %
Time to sober (from first drink)
0.0746 / 0.015
= 4.97 hrs
How it works
The Widmark formula estimates blood alcohol concentration from the amount of alcohol consumed, body weight, sex and time elapsed. The sex-specific distribution constant r accounts for different body water percentages. Alcohol is eliminated at approximately 0.015 %/hour on average. BAC is expressed as grams per 100 mL of blood (g/dL), so 0.08 % = 0.08 g/dL.
Formula
Widmark formula
BAC = (A × 5.14) / (W × r) − 0.015 × H
- A
- Pure alcohol (fl oz)
- W
- Body weight (lbs)
- r
- Widmark factor (0.73 M, 0.66 F)
- H
- Hours elapsed since first drink
This BAC estimate is for educational purposes only. Do not use it to determine whether it is safe or legal to drive. Individual elimination rates vary widely. The only reliable way to measure BAC is with a breathalyser or blood test. Never drink and drive.
Frequently Asked Questions
What is one standard US drink?
One US standard drink contains 0.6 fl oz (14 g) of pure alcohol — roughly a 12 oz beer at 5 %, a 5 oz glass of wine at 12 %, or a 1.5 oz shot of 80-proof spirits.
How accurate is the Widmark formula?
It is an estimate. Individual elimination rates vary from about 0.010–0.020 %/hr depending on body composition, liver health, food intake and genetics. The formula is most accurate when applied on an empty stomach; food significantly slows absorption.
Does body composition affect BAC?
Yes. Alcohol distributes through body water, not fat. People with higher muscle-to-fat ratios have more body water and therefore lower peak BAC for the same amount of alcohol.