How to Calculate Blood Alcohol Level: Complete Guide (2026)

Understanding your Blood Alcohol Concentration (BAC) isn't just about avoiding a ticket—it's about making life-saving decisions. Alcohol affects everyone differently, and the 'one drink per hour' rule is often dangerously inaccurate. In 2026, with stricter enforcement and lower limits in some areas, knowing your numbers is more important than ever.

What Is Blood Alcohol Concentration (BAC)?

BAC refers to the percentage of alcohol (ethanol) in your bloodstream. A BAC of 0.10% means that 0.1% of your bloodstream is composed of alcohol. While this sounds small, it has profound effects on your brain and motor skills.

How to Calculate BAC: The Science

The most scientifically accepted method for estimating BAC is the **Widmark Formula**. Developed by Swedish physician Erik Widmark, it accounts for body weight, gender, and the amount of pure alcohol consumed.

The simplified formula is: **BAC = [Alcohol(g) / (Body Weight(g) × r)] × 100 - (Time × 0.015)**

•**Alcohol(g)**: The weight of pure alcohol consumed.
•**Body Weight(g)**: Your weight in grams.
•**r**: The Widmark factor (constant for gender: ~0.68 for men, ~0.55 for women).
•**Time**: Hours since drinking began.
•**0.015**: The average rate at which your body eliminates alcohol per hour.

⚠️ WARNING: This formula is an ESTIMATE. It cannot account for individual metabolic rates, food in your stomach, or medication interactions. Never use a calculator to justify driving.

Step-by-Step Calculation Guide

1Determine the number of 'standard drinks' you've had. (1 drink = 12oz beer, 5oz wine, or 1.5oz shot).
2Convert your body weight to grams (Multiply lbs by 454).
3Apply the gender constant (0.68 for men, 0.55 for women) because women typically have less body water to dilute alcohol.
4Subtract 0.015% for every hour that has passed since you started drinking.
5The result is your estimated current BAC.

Skip the math. Use our Free Blood Alcohol Calculator →

BAC Levels & Effects

Here is what happens at different levels:

•**0.02%**: Relaxation, slight body warmth. Generally safe.
•**0.05%**: Exaggerated behavior, loss of small-muscle control (like focusing your eyes), impaired judgment. Driving is already dangerous.
•**0.08%**: LEGAL LIMIT in most US states. Muscle coordination poor (balance, speech, vision, reaction time). It is illegal to drive.
•**0.15%**: Very drunk. Major loss of balance, vomiting, confusion.
•**0.30%**: Stupor. You have little comprehension of where you are. Risk of passing out and death.

Tips to Sober Up

There is only one thing that lowers BAC: **Time**. Your liver processes alcohol at a constant rate. Coffee, cold showers, and water might make you *feel* more awake, but they do NOT lower the alcohol concentration in your blood.

Common Mistakes

People often underestimate the strength of their drinks. A 'pint' of high-ABV craft beer (7-9%) can count as 2 or even 3 standard drinks. Similarly, a heavy-handed pour of wine or a mixed cocktail often contains far more alcohol than the standard model assumes.

Key Takeaways

•Your BAC depends on weight, gender, drinks, and time.
•Standard drinks are smaller than you think (12oz beer, 5oz wine).
•The legal limit is 0.08%, but impairment starts sooner.
•Time is the only cure for a high BAC.
•When in doubt, don't drive.