Blood Alcohol Calculator

This is the Widmark formula. BAC percent = (grams of alcohol / (body weight in grams x r)) x 100, then subtract 0.015 for every hour since the first drink. r is the Widmark factor, the share of the body that is water: about 0.68 as a male average and 0.55 as a female average. Alcohol dissolves in water and not in fat, so two people of the same weight with different body composition reach different levels from the same drinks. One US standard drink holds 14 grams of pure alcohol. The 0.015 per hour elimination rate is an average; real rates range roughly from 0.010 to 0.020, which alone makes any estimate uncertain by a factor of two on the timing. What the formula ignores: how fast you drank, what was in your stomach, your liver, medication, tolerance, and the fact that alcohol takes 30 to 90 minutes to finish being absorbed, so your real level may still be climbing.

Is this accurate enough to decide whether to drive?

No. Nothing is, except not drinking. The Widmark estimate can be off by 0.02 or more in either direction, absorption may not be finished, and impairment begins below every legal limit. Treat any drinking as a reason to get a ride.

What is one standard drink?

In the US, about 14 grams of pure alcohol: 12 ounces of 5 percent beer, 5 ounces of 12 percent wine, or 1.5 ounces of 40 percent spirits. A pint of craft beer at 7.5 percent is roughly two standard drinks, and a generous pour of wine is often closer to two than one.

How long does alcohol stay in your system?

Blood alcohol falls at roughly 0.015 percent an hour, so a level of 0.08 takes about five and a half hours to reach zero. Breath and blood tests track that. Urine tests can show alcohol longer, and hair tests longer still.

Can I sober up faster with coffee, food or a shower?

No. Only time removes alcohol from your blood. Coffee makes a drunk person an awake drunk person, which is more dangerous, not less. Food eaten before drinking slows absorption and lowers the peak, but food eaten after does very little.

What is the legal BAC limit in the US?

0.08 percent in 49 states. Utah is 0.05. Commercial drivers are held to 0.04, and drivers under 21 face zero tolerance laws, where any measurable amount is an offense. You can also be charged below the limit if an officer judges you impaired.

Why do two people who drank the same have different levels?

Body weight, body composition, sex, how quickly they drank, what they had eaten, and differences in liver enzymes. Tolerance changes how drunk somebody feels but not how much alcohol is in their blood, which is why an experienced drinker can be well over the limit and seem fine.