What Is a BAC Calculator?
This BAC calculator estimates the blood alcohol content in your bloodstream from the drinks you have had, your weight, your gender, and how long you have been drinking. It is for anyone who wants a quick, ballpark sense of their alcohol level after a few drinks.
The tool uses the Widmark formula, the most widely accepted method for estimating BAC. It accounts for the body's natural elimination rate of roughly 0.015% per hour, so the longer it has been since your first drink, the lower your estimate.
How to Use the BAC Calculator
Select your gender
Choose Male or Female. This sets the Widmark distribution factor (0.68 for men, 0.55 for women) used in the calculation.
Enter your weight
Type your weight, then use the Metric / Imperial toggle to switch between kg and lbs. The value converts automatically when you change units.
Enter hours drinking
Set how many hours have passed since your first drink. This subtracts the alcohol your body has already metabolized.
Add your drinks
Tap a preset — Beer, Wine, or Spirits — to add a standard serving. Tap again to increase the count, or use Custom to enter a specific volume and ABV%.
Read your results
Your estimated BAC appears with a color-coded impairment level, a gauge, the time to sober, and your status against the US legal limit. Adjust quantities with the +/− and ✕ controls and results update in real time.
Features
Widmark Formula Estimate
Uses the standard Widmark formula with a 0.015%-per-hour elimination rate to estimate your current BAC.
Gender-Specific Calculation
Applies the correct distribution factor — 0.68 for men and 0.55 for women — since alcohol spreads through body water differently.
Metric and Imperial Weight
Enter your weight in kg or lbs; the toggle converts the value automatically when you switch units.
Standard Drink Presets
One-tap Beer (330ml, 5%), Wine (150ml, 12%), and Spirits (44ml, 40%) servings with realistic alcohol content.
Custom Drinks
Add any drink by entering its volume and ABV percentage when the presets do not match what you had.
Multiple Drinks with Quantity Controls
Stack several drinks in one list and fine-tune each with + / − and remove buttons, with grams shown per item.
Color-Coded BAC Gauge
A visual gauge marks exactly where your BAC falls across the impairment zones, from sober green to danger red.
Six Impairment Levels
Your result is mapped to one of six levels — from Sober / Minimal up to Danger Zone — each with a plain-language description.
Time to Sober
Estimates how long until your BAC returns to zero based on the average elimination rate.
US Legal Limit Comparison
Flags whether your estimate is over or under the US legal driving limit of 0.08% for quick reference.
BAC Impairment Levels
The calculator maps your estimated BAC to one of six color-coded levels so you can read the result at a glance:
0.00 – 0.02% · Sober / Minimal
Little to no noticeable effect.
0.02 – 0.05% · Slight
Relaxed feeling, mild impairment begins.
0.05 – 0.08% · Impaired
Reduced coordination and judgment.
0.08 – 0.15% · Legally Drunk
Significant impairment — over the US legal driving limit.
0.15 – 0.30% · Severely Impaired
Very dangerous, major loss of control.
0.30%+ · Danger Zone
Risk of blackout, alcohol poisoning, or death.
The Widmark Formula
The estimate uses the standard Widmark equation:
BAC = (Alcohol grams ÷ (Weight kg × 1000 × r)) × 100 − (0.015 × Hours)
Here r is the Widmark distribution factor (0.68 for men, 0.55 for women), and alcohol grams are calculated as Volume (ml) × ABV × 0.789, where 0.789 is the density of ethanol. The standard presets work out to roughly 13g of alcohol for beer and about 14g each for wine and spirits.
Frequently Asked Questions
How is BAC calculated with the Widmark formula?
The Widmark formula divides the total grams of alcohol you consumed by your body water (your weight times a distribution factor), converts it to a percentage, then subtracts roughly 0.015% for every hour since your first drink to account for what your body has already eliminated.
How accurate is this online BAC calculator?
The Widmark formula gives a reasonable estimate under standard conditions, but real BAC varies with food intake, individual metabolism, medication, liver health, and hydration — none of which the formula captures. Treat every result as an estimate only, never as a measured reading.
Why does gender affect the BAC calculation?
Alcohol distributes only in body water. Women generally have a lower percentage of body water than men of the same weight, so the same drinks produce a higher BAC. The Widmark formula reflects this with different distribution factors: 0.68 for men and 0.55 for women.
How long does it take for BAC to reach zero?
The time-to-sober estimate assumes your body clears about 0.015% BAC per hour, so it divides your current estimate by that rate. This is an average — your real metabolism may be faster or slower. Only time lowers BAC; coffee, water, and food do not speed up alcohol elimination.
What BAC is over the legal driving limit?
The calculator compares your estimate against the US legal limit of 0.08%. Limits vary by region — for example, 0.05% across much of Europe and Australia and 0.03% in Japan, with zero-tolerance rules in some places. Always check your local laws before driving.
Can I use this to decide whether to drive?
No. This tool provides an estimate only and must never be used to judge whether it is safe or legal to drive. Even a BAC below the legal limit can impair your driving. If you have consumed any alcohol, the safest choice is not to drive.
No comments yet. Be the first to comment!