BAC calculator
This BAC calculator estimates blood alcohol from your weight, what you drank and how long ago you started. It gives an estimate and cannot measure the alcohol in your blood. Never use it to decide whether to drive.
Your estimated BAC
0.000estimate only
Do not drive. Impairment starts before any legal limit, and no calculator can tell you that you are safe.
- Call a ride or a sober friend.
- Stay where you are until you have slept.
How this BAC calculator works
The estimate uses the Widmark formula: the grams of alcohol you drank, divided by your body weight times a body water constant, minus the alcohol your body has already cleared. One US standard drink holds 14 grams of pure alcohol. The constant is 0.68 for men and 0.55 for women, and the body clears about 0.015 of blood alcohol per hour on average.
- 12 fl oz beer, 5% ABV = 1 standard drink
- 5 fl oz wine, 12% ABV = 1 standard drink
- 1.5 fl oz distilled spirits, 40% ABV (80 proof) = 1 standard drink
Elimination rates vary from person to person, and NHTSA notes that so many factors affect BAC that it is very difficult to judge your own. That is why the figure is shown as an estimate.
BAC and the legal alcohol limit
In every state covered here, the legal alcohol limit for drivers 21 and over is 0.08. Lower limits apply to drivers under 21 and to commercial drivers; choose a state above to see them on the result.
BAC chart by weight and number of drinks
Estimated BAC one hour after the first drink, from the same formula, for standard drinks. Use the calculator above for your own numbers.
| Weight | 1 drink | 2 drinks | 3 drinks | 4 drinks | 5 drinks | 6 drinks |
|---|---|---|---|---|---|---|
| 100 lb | 0.030 | 0.076 | 0.121 | 0.167 | 0.212 | 0.257 |
| 120 lb | 0.023 | 0.061 | 0.098 | 0.136 | 0.174 | 0.212 |
| 140 lb | 0.017 | 0.050 | 0.082 | 0.115 | 0.147 | 0.180 |
| 160 lb | 0.013 | 0.042 | 0.070 | 0.098 | 0.127 | 0.155 |
| 180 lb | 0.010 | 0.035 | 0.061 | 0.086 | 0.111 | 0.136 |
| 200 lb | 0.008 | 0.030 | 0.053 | 0.076 | 0.098 | 0.121 |
| 220 lb | 0.006 | 0.026 | 0.047 | 0.068 | 0.088 | 0.109 |
| 240 lb | 0.004 | 0.023 | 0.042 | 0.061 | 0.080 | 0.098 |
| Weight | 1 drink | 2 drinks | 3 drinks | 4 drinks | 5 drinks | 6 drinks |
|---|---|---|---|---|---|---|
| 100 lb | 0.041 | 0.097 | 0.153 | 0.209 | 0.266 | 0.322 |
| 120 lb | 0.032 | 0.079 | 0.125 | 0.172 | 0.219 | 0.266 |
| 140 lb | 0.025 | 0.065 | 0.105 | 0.145 | 0.185 | 0.226 |
| 160 lb | 0.020 | 0.055 | 0.090 | 0.125 | 0.160 | 0.195 |
| 180 lb | 0.016 | 0.047 | 0.079 | 0.110 | 0.141 | 0.172 |
| 200 lb | 0.013 | 0.041 | 0.069 | 0.097 | 0.125 | 0.153 |
| 220 lb | 0.011 | 0.036 | 0.062 | 0.087 | 0.113 | 0.138 |
| 240 lb | 0.008 | 0.032 | 0.055 | 0.079 | 0.102 | 0.125 |
Sources
Standard drink: National Institute on Alcohol Abuse and Alcoholism. Formula constants: peer reviewed studies in PubMed Central, elimination rate. On estimating your own BAC: NHTSA. Read on 2026-10-31.