BAC Calculator
Estimate blood alcohol content over time using the Widmark formula.
About BAC Calculator
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
Worked example
With the default values below, BAC Calculator returns BAC now of 0.0521. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Biological sexone of Male, Female
- Male
- Body weightaccepts 50–600 lbs
- 170 lbs
- Weight unitone of lbs, kg
- lbs
- Number of standard drinksaccepts 0–50
- 3
- Hours since first drinkaccepts 0–24
- 1.5
- Project BAC until sober (hours ahead)accepts 0–24
- 6
Results
- 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
- 1Widmark constant (r)= 0.73 (male)
- 2Pure alcohol= 1.80 oz
- 3Peak BAC= 0.0746 %
- 4BAC after elimination= 0.0521 %
- 5Time to sober (from first drink)= 4.97 hrs
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- 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.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.