BAC Calculator

The formula, and what it assumes

BAC% = (alcohol grams ÷ (body weight in grams × r)) × 100 − 0.015 × hours

r is how widely alcohol distributes through body water: 0.68 for men and 0.55 for women, which is why the same drinks produce a higher number for a woman of the same weight. The 0.015 is the elimination rate — the roughly constant amount of alcohol percentage your body clears per hour. A US standard drink is 14 grams of pure alcohol.

Two things the formula does not do. It assumes the alcohol is already absorbed, so a drink taken five minutes ago is not fully counted; and it assumes an average body, so any individual result can land well above or below it. Treat the output as an order of magnitude, not a breath test.

Why "how many drinks" is the wrong question

Most BAC calculators ask for a number of drinks and quietly treat each one as a standard drink. That is where they go wrong, because pours are not standard. A 12 oz regular beer, a 5 oz glass of table wine, and a 1.5 oz shot of 80-proof spirits all hold exactly one standard drink — but a pint of 7.1% craft IPA holds 1.89 of them, and a generous 8 oz pour of 13.5% wine holds 1.80.

Two pints of that IPA are 3.79 standard drinks, not two — enough to put the 180 lb man at 0.080%, exactly on the legal line, one hour in. That is why this calculator asks for the size of the glass as well as the count, and why the pour-by-pour reference table lives inside it rather than in these paragraphs.

What the numbers mean

• 0.02% — the level at which measurable impairment of divided attention begins.
• 0.05% — reduced coordination and reaction time; the legal limit in Utah and in many other countries.
• 0.08% — the per se limit for drivers 21 and over in most of the US. Commercial drivers are held to 0.04%, and drivers under 21 are subject to zero-tolerance laws with limits as low as 0.01–0.02%.
• 0.15% and above — substantial impairment of balance, speech, and memory; most states add enhanced penalties.
• 0.30% and above — a medical emergency. Loss of consciousness, suppressed breathing, and the risk of alcohol poisoning are real at this level.

Penalties scale with the number as well as with the driving: many states increase the sanction at 0.15% or 0.20%, and implied-consent laws mean refusing a test carries its own consequence.

The only thing that lowers BAC

Time. At roughly 0.015% per hour, the 0.071% above takes 4 hours 44 minutes to reach zero, and the 0.098% example takes 6 hours 32 minutes. Coffee, cold showers, energy drinks, and food do not speed that up — caffeine makes you a more alert drunk person, not a sober one. Food before or during drinking slows absorption, which lowers the peak, but once the alcohol is in the blood only the liver clears it.

Common mistakes

• Counting pours as standard drinks. A generous wine pour is nearly two.
• Assuming "I feel fine" means "I am under". Impairment starts well below 0.08%, and subjective intoxication is a poor guide in either direction.
• Using elapsed hours instead of drinking hours. The clock starts when drinking starts, not when it stops.
• Forgetting the next morning. At 0.098% it takes more than six hours to reach zero; "sleeping it off" for four hours does not finish the job.

How to use this calculator

1. Choose the body type used for the estimate and enter your weight.
2. Enter how many drinks you had.
3. Enter the size of each pour and its ABV — the label on the can or bottle has it.
4. Enter how many hours ago you started drinking.
5. Read the BAC, the hours until you are under 0.08%, and the hours until zero. Then arrange a ride.

Frequently asked questions

How long does it take for one drink to leave your system?

About an hour to an hour and a half for a standard drink in an average adult — the body clears roughly 0.015% BAC per hour regardless of how much you drank.

Is 0.08% the legal limit everywhere?

It is the per se limit for drivers 21 and over in most US states. Utah uses 0.05%, commercial drivers are held to 0.04%, and drivers under 21 face zero-tolerance limits as low as 0.01%.

Why is a woman's BAC higher after the same drinks?

Body water. Alcohol distributes through water rather than fat, and the average distribution factor is lower for women (0.55 versus 0.68), so the same amount of alcohol produces a higher concentration.

Does eating lower your BAC?

Food slows absorption, so it lowers the peak and spreads it out — but it does not clear alcohol that is already in the blood, and it does not change the elimination rate.

Can I trust this number before driving?

No. This is a population estimate with wide individual variation, and impairment begins below the legal limit. No figure on this page means driving is safe.

What raises BAC faster than expected?

Drinking quickly, drinking on an empty stomach, lower body weight, some medications, and being female all push the number higher than a rough guess would suggest.

Data sources: Estimates use the Widmark formula with distribution factors of 0.68 (male) and 0.55 (female) and an elimination rate of 0.015% per hour — the standard forensic approximation, with real elimination ranging from about 0.010% to 0.020% per hour. A US standard drink is 14 grams of pure alcohol (12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 80-proof spirits); pure alcohol is taken as 23.33 grams per fluid ounce. Absorption, carbonation, medication, food, and liver function are not modeled, so individual results vary widely. This is an estimate, not a breath or blood test, and it is not a basis for deciding whether to drive — no amount of alcohol is required for a DUI if your driving is impaired. If you have been drinking, do not drive. Nothing you enter is stored; all calculations run in your browser. Related: water intake calculator, body fat calculator.