Blood Alcohol Content Calculator

Estimate your blood alcohol content (BAC) using the Widmark formula. Understand impairment at different BAC levels, legal limits by jurisdiction, and how long until your BAC returns to zero. For educational purposes only — never drive impaired.

⚠️ Educational Use Only: BAC varies significantly by individual. Never use this calculator to decide whether it's safe to drive. If in doubt, don't drive — use a rideshare or designated driver.
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Your Estimated BAC

Current BAC —
Impairment Level —
Legal to Drive? —
Hours Until Sober (0.00%) —

BAC Impairment Levels

BAC %LevelEffects

Legal BAC Limits by Country

Country / RegionLimit (BAC %)
USA (most states)0.08% (commercial: 0.04%)
USA (Utah)0.05%
Canada0.08% (warn range: 0.05%)
UK (England, Wales, NI)0.08%
UK (Scotland)0.05%
Australia0.05%
Most of Europe0.05%
Japan, Norway, Sweden0.03%
UAE, India (some states)0.00%

The Widmark Formula for BAC

BAC is estimated using the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s:

BAC = (A × 5.14 / W × r) − 0.015 × H

Where: A = ounces of pure alcohol consumed, W = body weight (pounds), r = Widmark constant (0.73 male / 0.66 female), H = hours since drinking started.

The body processes approximately 0.015% BAC per hour — equivalent to about one standard drink per hour. This rate cannot be accelerated by any method.

Standard Drink Sizes (US)

  • Beer: 12 oz at 5% alcohol = 0.6 oz pure alcohol
  • Wine: 5 oz at 12% alcohol = 0.6 oz pure alcohol
  • Spirits/liquor: 1.5 oz at 40% alcohol = 0.6 oz pure alcohol

All three equal approximately one standard drink (0.6 oz pure alcohol).

Frequently Asked Questions

In all US states, a BAC of 0.08% or higher is legally impaired for adult drivers. Many states have zero-tolerance laws for drivers under 21 (typically 0.01–0.02% BAC). Commercial drivers face a lower limit of 0.04%. Some countries use 0.05% as the legal limit. However, driving ability is measurably impaired starting at BAC of 0.02–0.05% — well below the legal threshold.

The liver metabolizes alcohol at roughly 0.015% BAC per hour — equivalent to about one standard drink per hour for a 150 lb person. This rate is relatively constant and cannot be meaningfully accelerated by coffee, cold water, food, or exercise. Food consumed before or during drinking slows alcohol absorption but does not speed elimination. Only time clears alcohol from your system.

Food in the stomach significantly slows alcohol absorption into the bloodstream, resulting in lower peak BAC and a slower rise. A meal high in fat and protein is most effective. However, food delays the BAC curve — it does not reduce total alcohol absorbed or speed up elimination. Eating after drinking has minimal effect on BAC compared to eating before or during.