DUI BAC Calculator

After a DUI arrest most people want to know one thing: was I actually over the limit? This tool gives you a rough idea using the Widmark formula, the same basic arithmetic experts start from. It will not tell you what your BAC was. It will show you a range, and that range is usually wide.

What the number does and does not mean

You can be convicted below 0.08. Vehicle Code section 23152(a) covers driving under the influence with no number attached — the prosecution argues impairment from the officer's observations, the field tests, and the driving pattern. Subsection (b) is the separate 0.08 charge. Most cases are filed as both, so an estimate under the limit does not mean there is no case.

Different limits apply to different drivers. 0.01 if you are under 21 or on DUI probation. 0.04 in a commercial vehicle with a commercial licence. 0.04 carrying passengers for hire.

Timing matters more than people expect. The charge is being over the limit while driving, not an hour later at the station. Alcohol is still absorbing for a while after the last drink, so a test taken later can read higher than you were at the wheel. That gap is one of the places these cases get won.

This has no evidentiary value. No court will accept a website calculation. What matters is the actual breath or blood result, whether the machine was calibrated, whether the blood was drawn and stored properly, and whether the stop was lawful in the first place.

Why the range is so wide

The formula assumes an average relationship between body weight and body water. Real people vary — by build, by how much they had eaten, by how quickly they drank, by medication, by how their liver processes alcohol that night. Two people the same weight drinking the same amount can end up meaningfully far apart. That is why this shows a band instead of a figure, and why the band is honest about how little it pins down.