BAC Calculator — Blood Alcohol Content Estimator

How does the BAC calculator work?

Enter your body weight, sex, drink type, number of drinks, and hours since you started drinking. The calculator applies the Widmark formula — the standard forensic toxicology method since 1932 — to estimate your current BAC, the time until you reach 0.00 g/dL, and how your BAC compares to legal driving limits in different countries.

The Widmark formula explained

BAC (g/dL) = (alcohol_grams × 100) / (r × body_weight_grams) − β × hours. The Widmark r-factor (0.68 for men, 0.55 for women) reflects the share of body weight into which alcohol distributes — essentially body water, not fat. β (0.015 g/dL/hr) is the average liver metabolism rate. A US standard drink = 14g pure alcohol (12 oz beer / 5 oz wine / 1.5 oz spirit, all ~5-12-40% ABV respectively).

Global legal limits

The table below lists the threshold at which each country penalises drink-driving, with a link to its statute. Elsewhere: 0.0 g/L in the Czech Republic, Hungary and much of Latin America; 0.2 g/L in Sweden, Norway and Poland; 0.5 g/L in most of the EU; 0.8 g/L in the United States, England and Canada.

Legal drink-drive limits by country (g/L of blood)

Threshold at which the law penalises, in grams of alcohol per litre of blood (0.5 g/L = 0.05 g/dL = 50 mg/100 mL). Breath equivalents follow each country’s statutory ratio. Every figure links to the law it comes from.

• United States: Every state applies a 0.08 g/dL per se limit (Utah: 0.05). Commercial drivers: 0.04 (49 CFR 382.201). Drivers under 21: 0.02 in every state (23 U.S.C. § 161).
• United Kingdom (England, Wales, N. Ireland): England, Wales and Northern Ireland: 80 mg per 100 mL of blood, 35 µg per 100 mL of breath. Scotland is stricter: select it separately.
• Scotland: Scotland: 50 mg per 100 mL of blood, 22 µg per 100 mL of breath since December 2014.
• Canada: Criminal offence at 80 mg per 100 mL within two hours of driving. Provinces add administrative sanctions at lower levels (commonly 0.05) and zero tolerance for new drivers.
• Ireland: "Specified persons" — learner permit holders, holders of a first driving licence and drivers of buses, taxis, HGVs and other categories listed in s. 3 — are limited to 20 mg per 100 mL.
• Australia: Limits are set by each state, with the same pattern nationwide: under 0.05 for open/full licences, zero for learner, provisional and probationary drivers and for heavy-vehicle, bus and taxi drivers.
• New Zealand: Drivers under 20: zero. 50-80 mg per 100 mL (250-400 µg per litre of breath): infringement fine and demerit points; above 80 mg: criminal offence.
• South Africa: 0.05 g per 100 mL of blood (0.24 mg per litre of breath) in general; 0.02 g per 100 mL (0.10 mg per litre of breath) for professional drivers (section 32).

Legal texts checked on 22 September 2026.

Factors that affect BAC

Several factors influence your BAC beyond weight and gender: food in your stomach (slows alcohol absorption and lowers the peak), carbonated mixers (speed absorption), fatigue (increases impairment for same BAC), medications (may amplify effects), and tolerance (affects perceived impairment but NOT actual BAC). The liver can only process ~one standard drink per hour regardless of other factors.