Our BAC calculator helps you estimate your Blood Alcohol Concentration based on your sex, weight, number of standard drinks, and time since your first drink. Use it to plan ahead, understand impairment, and make safer choices.
What is BAC and why it matters
Blood Alcohol Concentration (BAC) is the percentage of alcohol present in your bloodstream. Even small increases in BAC can affect judgment, coordination, and reaction time. In many regions, a BAC of 0.08% is the legal limit for driving, but impairment often begins well below that threshold. Knowing your estimated BAC can help you recognize risk and choose alternatives like rideshares, public transport, or a designated driver.
How our BAC calculator works
The calculator uses a commonly referenced Widmark-based approach. You provide your sex, weight, the number of standard drinks consumed, and the hours since your first drink. The tool converts standard drinks into an estimate of pure alcohol and factors in average alcohol metabolism to display an estimated BAC. It also recognizes different regional definitions of a standard drink—US (14 g), UK (8 g), and Australia (10 g) of pure alcohol—so your entry aligns with local guidelines.
What counts as a standard drink?
- US: 14 g pure alcohol (roughly 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits).
- UK: 8 g pure alcohol (1 UK unit per 8 g).
- Australia: 10 g pure alcohol per standard drink.
Labels and pours vary. When in doubt, round up and be conservative to avoid underestimating your BAC.
Key factors that influence BAC
- Sex: Average body water composition differs by sex, affecting alcohol distribution.
- Weight: Higher body mass generally dilutes alcohol over a larger volume.
- Amount consumed: More alcohol raises BAC.
- Time: Your body metabolizes alcohol over time; typical average is about 0.015 BAC per hour.
- Food and pace: A full stomach and slower drinking can reduce peak BAC, though the calculator assumes average conditions.
How to use the BAC calculator
- Select your sex and enter your weight with the correct unit (lb or kg).
- Choose your region’s standard drink definition (US, UK, or Australia).
- Enter the total number of standard drinks consumed.
- Enter the hours since your first drink.
- Submit to view your estimated BAC and suggested timelines.
Interpreting your results
If your estimated BAC is above your local legal limit, do not drive. Even below the limit, you may be impaired. The calculator may also estimate how long it might take to return to 0.00% BAC or below common legal thresholds based on typical metabolism. Individual rates vary considerably, so always err on the side of caution.
Limitations and safety reminders
This BAC calculator provides an estimate, not a definitive measurement. It does not account for personal health conditions, medications, fatigue, hydration, or individual metabolic differences. Breathalyzers and blood tests provide more accurate readings, but even those can vary. The safest approach is simple: if you’ve been drinking, choose not to drive.
Plan ahead for a safer night
- Arrange a designated driver or rideshare before you start drinking.
- Eat before and during drinking to moderate absorption.
- Drink water between alcoholic beverages.
- Aim for lower-ABV options and smaller pours.
Use this BAC calculator as a planning tool, not a green light. Your safety—and that of others—matters more than any estimate.