This calculator provides estimates only. Never drive after drinking. BAC varies significantly between individuals. No calculator can guarantee you are safe or legal to drive.
BAC Calculator
Widmark Formula · Estimates only: never drive after drinking
lbs
hrs
Time elapsed since you started drinking
Enter your weight, sex, drinks consumed, and time since first drink.
Estimated BAC
0.000
% blood alcohol content
BAC Level
0.000.040.080.150.250.40+
Breakdown
Total alcohol consumed
Alcohol metabolized
Remaining alcohol
Widmark factor (r)
Time to reach...
Legal limit (0.08%)
Caution zone (0.05%)
Completely sober (0.00%)
BAC Levels: What They Mean
By the Widmark formula, two standard drinks put a 160-lb man at about 0.057% BAC and a 140-lb woman at about 0.080% once fully absorbed, before the body clears roughly 0.015% per hour. This calculator gives an estimate for education only. It cannot tell you that you are safe or legal to drive. If you have been drinking, do not drive.
Blood alcohol content (BAC) is the concentration of alcohol in the bloodstream, expressed as a percentage. A BAC of 0.08% means 0.08 grams of alcohol per 100 mL of blood. This is the legal driving limit in the United States and many other countries. However, impairment begins well below this threshold: at 0.02 to 0.04%, judgment and reaction time are already measurably affected.
| BAC Level | Effects | Legal Status (US) |
|---|---|---|
| 0.01 to 0.03% | Mild relaxation, slight warmth, minimal impairment | Under 0.08%, but a DUI arrest is still possible; illegal under 21 |
| 0.04 to 0.05% | Relaxed, slight judgment impairment, lowered inhibitions | At or over the 0.04% commercial limit; 0.05% is the Utah limit |
| 0.06 to 0.07% | Impaired judgment, reduced coordination, slower reflexes | Illegal in Utah; impaired driving charge possible anywhere |
| 0.08% | Significant impairment of coordination, reaction time, judgment | DUI threshold (US) |
| 0.09 to 0.15% | Slurred speech, poor balance, severely impaired driving ability | Illegal to drive |
| 0.16 to 0.30% | Confusion, disorientation, nausea, blackout risk | Seriously illegal |
| 0.31%+ | Loss of consciousness, life-threatening respiratory depression | Medical emergency |
The Widmark Formula
BAC = (alcohol in grams) / (body weight in grams × Widmark factor r) × 100, minus (metabolism rate × hours). The Widmark factor r is 0.68 for men and 0.55 for women, reflecting differences in body water distribution. Women have lower body water percentage and less alcohol dehydrogenase enzyme, resulting in higher BAC for the same intake. This formula was developed by Swedish physician Erik Widmark in the 1930s and remains the foundation of forensic BAC estimation.
Standard Drink Definition
One standard US drink contains 14 grams (0.6 fl oz) of pure alcohol: a 12 oz regular beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or 1.5 oz of 80-proof spirits at 40% ABV. Many craft beers (7-9% ABV) and large pours count as 1.5-2 standard drinks. Cocktails with multiple spirits can equal 2-3 standard drinks. Knowing standard drink equivalents helps with accurate tracking.
Alcohol Metabolism Rate
The liver metabolizes alcohol at a nearly constant rate of approximately 0.015% BAC per hour (about 1 standard drink per hour for most adults). Nothing significantly accelerates this rate: not coffee, exercise, cold showers, or food after drinking. Food before or while drinking slows alcohol absorption, reducing peak BAC, but does not change elimination speed. Only time reduces BAC.
Why BAC Varies Between People
Same amount of alcohol, different BAC: body weight (heavier = lower BAC), body composition (more muscle = lower BAC, since muscle holds more water than fat), sex (women typically reach higher BAC), food intake (slows absorption), alcohol tolerance (affects perception but not actual BAC), liver health, genetics (ADH enzyme variants), and medications. This calculator accounts for weight and sex but not all individual variables.
Estimated Peak BAC by Weight and Number of Drinks
Percent BAC once all the alcohol is absorbed, before any is eliminated. One drink is a US standard drink of 14 g of alcohol. Subtract about 0.015 for every hour since your first drink. Real values vary widely from person to person.
Men (Widmark r = 0.68)
| Weight | 1 drink | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| 120 lb | 0.038 | 0.076 | 0.113 | 0.151 | 0.189 | 0.227 |
| 140 lb | 0.032 | 0.065 | 0.097 | 0.130 | 0.162 | 0.195 |
| 160 lb | 0.028 | 0.057 | 0.085 | 0.113 | 0.142 | 0.170 |
| 180 lb | 0.025 | 0.050 | 0.076 | 0.101 | 0.126 | 0.151 |
| 200 lb | 0.023 | 0.045 | 0.068 | 0.091 | 0.113 | 0.136 |
| 220 lb | 0.021 | 0.041 | 0.062 | 0.083 | 0.103 | 0.124 |
| 240 lb | 0.019 | 0.038 | 0.057 | 0.076 | 0.095 | 0.113 |
Women (Widmark r = 0.55)
| Weight | 1 drink | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| 120 lb | 0.047 | 0.094 | 0.140 | 0.187 | 0.234 | 0.281 |
| 140 lb | 0.040 | 0.080 | 0.120 | 0.160 | 0.200 | 0.241 |
| 160 lb | 0.035 | 0.070 | 0.105 | 0.140 | 0.175 | 0.210 |
| 180 lb | 0.031 | 0.062 | 0.094 | 0.125 | 0.156 | 0.187 |
| 200 lb | 0.028 | 0.056 | 0.084 | 0.112 | 0.140 | 0.168 |
| 220 lb | 0.026 | 0.051 | 0.077 | 0.102 | 0.128 | 0.153 |
| 240 lb | 0.023 | 0.047 | 0.070 | 0.094 | 0.117 | 0.140 |
The Widmark Formula Step by Step
BAC (%) = alcohol in grams ÷ (body weight in grams × r) × 100 − 0.015 × hours since the first drink. The factor r is the share of body weight that alcohol spreads into: 0.68 on average for men and 0.55 for women, which is why a woman of the same weight usually reaches a higher BAC.
Example: a 160-lb man has four 12 oz beers at 5% over 2 hours.
- Alcohol: 4 × 14 g = 56 g.
- Body weight in grams: 160 ÷ 2.205 = 72.6 kg, or 72,600 g.
- Peak BAC: 56 ÷ (72,600 × 0.68) × 100 = 0.113%.
- Elimination: 0.015 × 2 hours = 0.030.
- Estimate now: 0.113 − 0.030 = 0.083%, over the 0.08% limit. Reaching zero takes about 5.6 more hours.
Elimination rates in healthy adults commonly range from about 0.010% to 0.020% per hour, so the same drinks can leave two people hours apart.
US Driving Limits and Why No Calculator Can Clear You to Drive
- 0.08% is the per se limit for drivers 21 and older in every state except Utah, where it is 0.05%.
- 0.04% applies to commercial drivers operating a commercial vehicle under federal rules.
- Drivers under 21 face zero-tolerance laws, with limits of 0.02% or lower.
- Below the limit is not a safe harbor. You can be arrested for impaired driving at any BAC if your driving or behavior shows impairment.
The formula cannot know how fast you absorbed the drinks, your real pour sizes, your own elimination rate, medications or what you ate. BAC can also keep rising for 30 to 90 minutes after the last drink. That is why this calculator can never tell anyone they are safe or legal to drive. Plan a ride before you start drinking. For converting beer, wine and spirits into standard drinks, see the alcohol unit calculator.
Method and sources. Widmark formula (Widmark EMP, 1932): BAC = A ÷ (W × r) × 100 − βt, with A in grams, W in grams, r = 0.68 for men and 0.55 for women, and β = 0.015% per hour. Standard drink of 14 g: NIAAA. Limits: NHTSA; commercial drivers 49 CFR 382.201 (FMCSA); Utah Code 41-6a-502. Every BAC figure above was computed with this formula. Estimates only, never a basis for deciding to drive.
This calculator is for educational and harm-reduction purposes only. BAC estimates have significant individual variation (plus or minus 20-30%). Never use this calculator to determine whether it is safe or legal to drive. If you have been drinking, do not drive. Call a rideshare, taxi, or designated driver.
BAC Calculator Questions
BAC is calculated using the Widmark formula: BAC = (grams of alcohol consumed / (body weight in grams × Widmark factor r)) × 100, minus (elimination rate × hours drinking). The Widmark factor r represents body water ratio: 0.68 for men, 0.55 for women. The standard elimination rate is approximately 0.015% per hour. For example: a 160 lb (72.6 kg) man who drinks 2 standard drinks (28g alcohol) over 2 hours has a BAC of approximately: (28 / (72,600 × 0.68)) × 100 − (0.015 × 2) = 0.057% − 0.03% = 0.027%.
In the United States, every state except Utah sets the limit at 0.08% BAC for drivers 21 and older; Utah's limit is 0.05%. For commercial drivers (CDL holders), the limit is 0.04%. For drivers under 21, most states enforce zero-tolerance laws with limits of 0.00-0.02%. Many other countries, including most of Europe and Australia, use 0.05%, and a few, such as the Czech Republic and Hungary, allow no alcohol at all. Remember that impairment begins well before 0.08%: even at 0.04%, reaction time and judgment are measurably affected.
BAC drops at approximately 0.015% per hour through liver metabolism. This rate is relatively constant regardless of coffee, exercise, cold showers, or other interventions. Examples: starting BAC of 0.08% takes about 5.3 hours to reach 0.00%. Starting BAC of 0.15% takes about 10 hours. Starting BAC of 0.25% takes about 17 hours. Individual variation exists based on liver health and genetics, but these estimates are reasonably accurate for most healthy adults. Sleep does not accelerate alcohol metabolism: a person who passes out with a BAC of 0.20% will still have a significant BAC in the morning.
Women typically reach higher BAC for three reasons: lower body water percentage (alcohol distributes in body water, so less water means higher concentration), lower levels of alcohol dehydrogenase enzyme in the stomach (less first-pass metabolism before alcohol enters bloodstream), and typically lower body weight. The Widmark factor r is 0.68 for men and 0.55 for women, reflecting the body water difference. Body composition also matters within each sex: a lean, muscular man has more body water than an overweight man of the same weight, resulting in lower BAC for the same intake.
Yes, but only absorption speed, not elimination. Eating before or while drinking significantly slows alcohol absorption from the stomach into the bloodstream. This reduces peak BAC and delays when peak BAC is reached. A full stomach can reduce peak BAC by 30-50% compared to drinking on an empty stomach. However, the total amount of alcohol processed by the liver is the same: food does not make you sober faster, it only reduces how high your BAC gets. Fatty and protein-rich foods slow absorption most effectively. Eating after drinking is almost ineffective since alcohol is already in the bloodstream.
No. This calculator provides estimates with significant uncertainty margins. Individual variation in alcohol metabolism, absorption, and tolerance means actual BAC can differ from calculated BAC by 20-30% or more. Additionally, impairment for driving begins below 0.08%: at 0.05-0.06%, reaction time, divided attention, and lane tracking are already measurably impaired. You can be charged with driving while impaired even below 0.08% if an officer observes impaired driving. The only safe approach is zero alcohol before driving. Use a rideshare, taxi, or designated driver.
In the United States, one standard drink contains 14 grams (0.6 fl oz) of pure alcohol. This equals: 12 oz regular beer (5% ABV), 8-9 oz malt liquor (7% ABV), 5 oz table wine (12% ABV), 3-4 oz fortified wine such as port or sherry (17% ABV), 1.5 oz (one shot) of 80-proof spirits (40% ABV). Note that many common drinks exceed one standard drink: a pint (16 oz) of 7% craft beer is 1.9 standard drinks; a 750 ml bottle of 12% wine is about 5 standard drinks; a large cocktail with 3 oz of spirits is 2 standard drinks. Serving sizes at bars are often larger than standard drink definitions.
Tolerance affects how you feel at a given BAC, not the actual BAC itself. A person with high alcohol tolerance may feel minimal impairment at 0.10% BAC, but their reaction time, coordination, and driving ability are just as impaired as someone who feels very drunk at the same level. This is why experienced drinkers who "don't feel drunk" are still dangerous drivers at elevated BAC: and why they may underestimate their impairment. Long-term heavy drinking does cause metabolic tolerance (the liver becomes slightly more efficient at metabolizing alcohol), but that does not make high BAC levels safe.
Sleep does not accelerate alcohol metabolism. BAC continues to drop at the same 0.015% per hour rate whether awake or asleep. This is why "sleeping it off" requires genuinely adequate time. If someone goes to sleep at midnight with a BAC of 0.15%, they will still be at about 0.045% at 7 AM, seven hours later, which is over the 0.04% limit for commercial drivers. They will not reach zero until about 10 AM. Morning-after driving with residual alcohol is a real and underappreciated risk. A useful rule: if you drank heavily the night before, do not drive until you have allowed sufficient metabolism time based on your estimated peak BAC.
BAC calculators have significant inherent uncertainty. The Widmark formula estimates have a reported accuracy of plus or minus 20-30% compared to measured BAC in studies. Key sources of variation: uncertainty in exact drink volumes and ABV, individual differences in alcohol absorption rate, body composition differences within each sex (lean vs. fat at the same weight), liver health and enzyme levels, genetics (ADH enzyme variants), medications that interact with alcohol metabolism, and stomach contents. Breath testers used by police have their own margin of error, and some cases are confirmed with a blood test. Never rely on any calculator to determine driving safety.
Using the Widmark formula with drinks taken close together, about 3 standard drinks for a 160-lb man (0.085%) and 2 for a 140-lb woman (0.080%). A 200-lb man reaches about 0.091% with 4 drinks. Drinking more slowly lowers the peak, but by only about 0.015 per hour, and many people are impaired well below 0.08%.
Yes. Utah lowered its limit to 0.05% for drivers 21 and older at the end of 2018, and it is the only state with a limit below 0.08%. Commercial drivers anywhere in the US are held to 0.04%, and drivers under 21 face zero-tolerance limits of 0.02% or lower.