What Is a BAC Calculator?
This calculator provides a rough estimate of Blood Alcohol Concentration (BAC) using the widely referenced Widmark formula, based on body weight, sex, number of standard drinks, and time elapsed. It's intended for general education about how these factors affect BAC — not as a tool to determine whether it's safe to drive or perform any activity.
How to Use the BAC Calculator
- Select your sex (used because average body water percentage differs between sexes in the Widmark formula).
- Enter your body weight.
- Enter the number of standard drinks consumed.
- Enter hours elapsed since your first drink.
The Widmark Formula
The subtraction term accounts for the body metabolizing alcohol at an average rate of about 0.015% BAC per hour.
Understanding "Standard Drinks"
A US standard drink contains about 14 grams of pure alcohol — roughly one 12 oz beer (5% ABV), one 5 oz glass of wine (12% ABV), or one 1.5 oz shot of spirits (40% ABV). Actual alcohol content varies by beverage, so this is only an approximation.
Why This Is Only an Estimate
- Actual BAC is affected by many factors this formula doesn't capture: food intake, medications, individual metabolism, hydration, and overall health.
- Impairment of judgment, reaction time, and coordination can begin well below the legal driving limit in many places.
- Individual tolerance does not reduce actual impairment or blood alcohol level, even if it feels that way.
Never Use This to Decide Whether to Drive
No calculator can safely tell you whether you're fit to drive or perform any task requiring full alertness. If you've been drinking at all, the safest choice is not to drive — arrange a rideshare, taxi, designated driver, or public transit instead.
Frequently Asked Questions
No. This tool provides only a rough estimate and cannot account for many factors that affect real impairment and BAC. Never use any calculator to decide whether to drive after drinking — if you've had any alcohol, arrange another way home.
In the US, a standard drink contains about 14 grams of pure alcohol — roughly a 12 oz beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits, though actual alcohol content varies by specific beverage and serving size.
The Widmark formula uses different body water distribution constants for men and women, reflecting average physiological differences that affect how alcohol is distributed in the body.
Yes — eating before or while drinking slows alcohol absorption, which affects peak BAC and timing, though this simplified formula doesn't account for it.
These estimates can vary meaningfully from actual BAC due to individual differences in metabolism, hydration, food intake, and other factors — they should never be relied on for safety-critical decisions like driving.