BAC Calculator

Weight (kg)

Gender Male Female

Standard drinks

Hours since drinking

Calculate BAC

One standard drink = 14g of pure alcohol (e.g. 355ml regular beer, 148ml wine, 44ml spirits).

BAC Calculator — Guide & Formula

Blood Alcohol Content (BAC) measures the concentration of alcohol in your bloodstream, expressed as grams of alcohol per decilitre of blood (g/dL). This free BAC calculator uses the Widmark formula to estimate your BAC based on weight, gender, number of drinks, and time elapsed.

Widmark formula

• BAC = (A × 5.14) / (W × r) − 0.015 × H
• A = grams of alcohol consumed (14g per US standard drink)
• W = body weight in pounds
• r = alcohol distribution ratio ≈ 0.73 for men, 0.66 for women
• H = hours elapsed since drinking began
• Body metabolises approximately 0.015 g/dL per hour

BAC levels and effects

BAC (g/dL)	Effect
0.00	Sober
0.02 – 0.04	Mild relaxation, slight warmth
0.05 – 0.07	Lowered inhibitions, mild impairment
0.08	Legal driving limit in most countries � reaction time slowed
0.08 – 0.15	Significant impairment — slurred speech, poor coordination
0.15 – 0.25	Severe impairment — confusion, nausea, vomiting
0.25 – 0.40	Stupor, risk of unconsciousness
0.40+	Risk of coma or death

What counts as one standard drink?

• Regular beer (5% ABV) – 355 ml (12 fl oz)
• Wine (12% ABV) – 148 ml (5 fl oz)
• Spirits / distilled liquor (40% ABV) – 44 ml (1.5 fl oz)
• All contain approximately 14 grams of pure alcohol

Factors that affect BAC

• Body weight: more body mass dilutes alcohol further
• Gender: women typically have less body water and different enzyme activity
• Food: eating before/during drinking slows alcohol absorption significantly
• Drink rate: faster drinking elevates BAC more quickly
• Hydration: dehydration concentrates blood alcohol
• Medications: many drugs interact with alcohol — consult your pharmacist

References

• Widmark, E.M.P. (1932). "Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung"
• National Institute on Alcohol Abuse and Alcoholism (NIAAA) — Standard Drink Definition
• "Forensic Issues in Alcohol Testing" — Garriott, J.C.