What Is a BAC Calculator?

A BAC calculator estimates your blood alcohol concentration — the percentage of alcohol in your bloodstream — based on the drinks you've consumed, your body weight, your biological sex, and the time since your first drink. It uses the Widmark formula, the method used in clinical and legal BAC estimation. Enter your inputs and the calculator returns an estimated BAC percentage along with reference points for what that level typically means.

This is a harm reduction tool. It gives you an educational estimate, not a medical reading. Individual metabolism varies — factors like food intake, medications, fatigue, and liver function all affect real BAC in ways this estimate cannot capture.

How to Use the BAC Calculator

1. Enter your body weight and biological sex: These two variables have the largest impact on BAC. Body weight determines how much water is available to dilute alcohol; biological sex affects both water percentage and alcohol metabolism rates.
2. Count standard drinks accurately: One standard drink = 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits. A large craft IPA at 8% ABV counts as 1.6 standard drinks per 12 oz. Check the label.
3. Enter time elapsed since your first drink: The liver clears roughly 0.015% BAC per hour. More time = lower estimated current BAC.
4. Read your estimated BAC: Use the number as an educational reference. For driving decisions, the only safe BAC is zero — this tool is not a substitute for that judgment.

Who Is This For?

• People trying to understand their tolerance and how body weight and biological sex affect how alcohol hits them — the same number of drinks produces very different BAC in different people.
• Event hosts calculating approximate guest BAC for safety planning — useful for estimating when a guest has likely metabolized a given amount of alcohol before driving.
• Anyone curious about the science of how weight, sex, and time interact to determine blood alcohol — this tool makes the Widmark formula interactive and visible.

Key Benefits

• 100% private: Your inputs are processed in your browser and never sent to any server.
• Free, no account required: Use it as many times as needed without signing up.
• No subscription, no paywall: Full results every time.
• Sex-adjusted calculation: Accounts for the biological difference in body water percentage between males and females — not a one-size-fits-all formula.

Common Use Cases

Understanding how drinks add up over time: Enter 3 drinks consumed over 2 hours vs. 3 drinks in 1 hour to see how the same consumption produces different estimated BAC depending on pace.

Seeing how weight affects BAC: A 120 lb person and a 220 lb person consuming the same drinks produces very different results — this tool makes that difference concrete and visible.

Planning a safe event: Event organizers can model rough BAC timelines for guests of different sizes to inform when to stop service or arrange transportation.

BAC Reference Levels

Frequently Asked Questions