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
Drink rate: faster drinking elevates BAC more quickly
Hydration: dehydration concentrates blood alcohol
Medications: many drugs interact with alcohol — consult your pharmacist
⚠ Always drink responsibly. Never drive after drinking alcohol. This calculator is for informational purposes only and does not constitute medical or legal advice.
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.
Blood Alcohol Content (BAC) is the concentration of alcohol in your 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 US, Canada (federal), and UK (England/Wales), though actual impairment begins well below this level.
BAC effects by level:
0.02–0.03%: Slight mood elevation, minor relaxation. Most people feel the first effects. Reaction time and judgment minimally affected.
0.05–0.06%: Noticeable relaxation, mild euphoria, reduced inhibition. Judgment and fine motor skills begin to be impaired. Driving risk increases — some countries (Australia, EU member states) use 0.05% as the legal limit.
0.08%: US/UK legal limit. Significant impairment of balance, speech, vision, reaction time, and judgment. Driving at this BAC is 7× more likely to cause a fatal crash than driving sober.
0.20%+: Confusion, vomiting, blackouts. Risk of choking on vomit. Medical emergency.
0.30%+: Loss of consciousness, respiratory depression. Can be fatal.
How to Use This Calculator Responsibly
This BAC calculator uses the Widmark formula, which is the same mathematical model used in most clinical and legal settings. However, it is an estimate — individual BAC varies based on factors the calculator can't account for: food in your stomach (slows alcohol absorption by up to 50%), genetics (some people metabolize alcohol faster), medications, fatigue, and tolerance (tolerance affects how drunk you feel, but not your actual BAC).
Never use a BAC calculator to decide whether to drive. The only safe BAC for driving is 0.00%. If you plan to drink, plan your transportation — designated driver, rideshare, or staying overnight. Many DUI arrests occur at BAC levels the driver felt was "fine."
The elimination rate of 0.015%/hour is an average — actual rates range from 0.010% to 0.025% per hour. A "slow metabolizer" who processes alcohol at 0.010%/hour takes 50% longer to sober up than the calculator estimates.
Frequently Asked Questions
Does eating before drinking lower your BAC?
Yes, significantly. Food in the stomach slows alcohol absorption into the bloodstream by 20–50%. Fat and protein are most effective. The effect delays the peak BAC rather than reducing how much alcohol you ultimately absorb — you'll still reach the same final BAC, but more slowly. Eating after you've already been drinking has little effect, since the alcohol has already been absorbed. The practical implication: drink more slowly and eat a proper meal before, not during, drinking.
How many drinks per hour can I have and stay below 0.08%?
The liver eliminates approximately one standard drink per hour for an average-sized person (the 0.015%/hour elimination rate). However, this varies by body weight and sex. A 130 lb woman may reach 0.08% after just 2 standard drinks, while a 200 lb man might need 4. The safest approach is tracking drinks with this calculator using your actual stats rather than relying on rules of thumb. Remember: feeling "okay" doesn't mean you're below the legal limit.
What counts as a standard drink?
In the US, one standard drink contains 14 grams of pure alcohol: 12 oz regular beer (5% ABV), 5 oz wine (12% ABV), or 1.5 oz distilled spirits/liquor (40% ABV/80 proof). Many cocktails, craft beers, and wines contain multiple standard drinks in a single serving. A pint (16 oz) of 7% craft IPA is 1.87 standard drinks. A large restaurant pour of wine (8 oz) is 1.6 standard drinks. Tracking actual alcohol content, not just number of drinks, is essential for accurate BAC estimation.
