Blood Alcohol Content (BAC) Calculator
This simplified calculator estimates your blood alcohol content (BAC) by selecting your drink type and quantity instead of calculating alcohol grams manually. Uses the Widmark formula with standard drink volumes. In the US, 0.08% BAC is the legal driving limit for adults 21+. Never drive if you've been drinking.
When to use this calculator
- You're leaving a party and want to know if you're safe to drive.
- You want to understand how long it takes to eliminate alcohol from your system.
- You're comparing how different drinks affect your BAC.
- You're educating friends or family about responsible drinking.
- You work in hospitality and want to guide customers about alcohol content.
Example: 80kg man, 2 beers 500ml, 1 hour after drinking
- Grams: 2 × 20g = 40g of alcohol.
- Initial BAC:
40 / (80 × 0.68)= 0.74 g/L. - After 1 hour:
0.74 - 0.15= 0.59 g/L. - Hours until zero:
0.59 / 0.15= 3.9 hours.
How it works
1 min readAlcohol Grams by Drink Type
| Drink | Grams |
|---|---|
| Beer 330ml (5% ABV) | 13g |
| Beer 500ml (5% ABV) | 20g |
| Wine 150ml (13% ABV) | 15.4g |
| Fernet 50ml (39% ABV) | 15.6g |
| Whisky 45ml (40% ABV) | 14.2g |
| Champagne 150ml (12% ABV) | 14.2g |
Widmark Formula
BAC = grams_alcohol / (weight × r) - 0.15 × hoursWhere r = 0.68 (males) or 0.55 (females).
US Drunk Driving Laws
In all 50 US states, the legal driving limit is 0.08% BAC for drivers 21+. For drivers under 21, most states enforce zero tolerance (0.02% or lower). Commercial drivers must stay below 0.04%. Violating these limits results in DUI charges, license suspension, and potential jail time.
Effects by BAC Level
| BAC (g/L) | Effect |
|---|---|
| 0.0–0.3 | Mild relaxation |
| 0.3–0.5 | Impaired judgment |
| 0.5–0.8 | Reduced coordination |
| 0.8–1.5 | Marked intoxication |
| 1.5–3.0 | Confusion, vomiting |
| >3.0 | Risk of coma or death |
Common Myths About Sobering Up
Safe Alternatives to Driving
Frequently asked questions
How long does it take for one beer to leave your system?
A standard 330ml beer (13g alcohol) in a 75kg person produces ~0.25 g/L BAC, which takes 1.5–2 hours to eliminate at the standard rate of 0.15 g/L per hour.
How long does alcohol stay in your bloodstream?
Your body eliminates alcohol at roughly 0.15 g/L per hour, regardless of food, coffee, or exercise. One standard drink (13–14g) takes about 1.5–2 hours to clear.
What is a standard drink in the US?
One standard drink = 330ml beer (5% ABV), 150ml wine (12% ABV), or 45ml spirits (40% ABV). Each contains roughly 13–14g of pure alcohol.
Can you fail a breathalyzer test after one beer?
Possibly. One beer produces a BAC around 0.02–0.04 g/L in most adults. A breath test is sensitive enough to detect this, though it's under the 0.08% legal limit for driving.
Why do women get drunk faster than men?
Women have less of the enzyme alcohol dehydrogenase (ADH) in their stomach, lower body water percentage, and higher body fat. At the same consumption, women's BAC is typically 20–30% higher than men's.
Does non-alcoholic beer have any alcohol in it?
True non-alcoholic beer is labeled 0.0% ABV and has negligible alcohol. However, some "low-alcohol" beers contain 0.5% ABV and technically have a trace amount.
How many drinks can you have and still drive safely?
The safest number is zero. A single drink (13–14g alcohol) can impair judgment and reaction time in some people. The legal limit is 0.08% BAC, but impairment begins much earlier.
Does eating before or during drinking affect your BAC?
Food slows alcohol absorption into the bloodstream, which delays the peak BAC and spreads it over more time. However, it doesn't reduce your final BAC—only time does.
How accurate is this BAC calculator?
The Widmark formula has a margin of ±20% due to variations in metabolism, food, medications, hydration, and genetics. Never use it to decide whether to drive: if you've been drinking, don't drive.
What should I do if I've been drinking and need to get home?
Call Uber/Lyft, a taxi, a friend, or use public transit. Many cities have drunk-driving prevention programs. A rideshare is the safest option—never gamble with driving after drinking.