How Breathalyzers Determine Your BAC
A breathalyzer measures the alcohol concentration in your breath and converts it to an estimated blood alcohol concentration (BAC). In most US states, a BAC of 0.08% or higher is illegal per se for drivers, while commercial drivers and drivers under 21 face much lower thresholds. This tool doesn't replace an actual breathalyzer — it's a reference guide using the Widmark formula to help you roughly gauge where you might stand.
How the Estimate Is Calculated
First, pure alcohol consumed (volume × ABV × 0.8) is divided by body weight and a sex-specific distribution constant to estimate peak BAC. Then, the average elimination rate of 0.015% per hour is subtracted based on hours elapsed to estimate your current level. Actual breathalyzer readings can differ from this estimate due to individual physiology, whether you've eaten, and breath conditions at the time of testing.
Below the Limit Doesn't Mean Safe
Even below 0.05%, alcohol can still slow reaction time and impair judgment. Staying under the legal threshold and being truly safe to drive are two different things. If you feel any lingering effects at all, don't drive — use public transit or a designated driver instead.
Frequently Asked Questions
In most US states, a BAC of 0.08% or higher is illegal per se for drivers 21 and older. Even below that, judgment and reaction time can already be impaired.
No. This tool estimates BAC using the Widmark formula, while a real breathalyzer directly measures alcohol in your breath — results can differ based on individual physiology and timing.
Even a 0% estimate carries margin for individual variation and calculation error. If you feel any lingering effects at all, don't drive — wait longer to be safe.