A blood alcohol concentration (BAC) chart shows the estimated BAC produced by a given number of standard drinks, adjusted for body weight and biological sex. It is built from the Widmark formula: BAC = (alcohol grams) ÷ (body weight kg × r), where r is roughly 0.68 for men and 0.55 for women. Quick reference for a 70 kg adult: 1 standard drink = ~0.02% BAC for a man, ~0.03% for a woman; 3 drinks in one hour = ~0.06% for a man, ~0.09% for a woman; 5 drinks in two hours = ~0.10% for a man, ~0.14% for a woman. Impairment by BAC: 0.02% — relaxation, mild mood lift; 0.05% — reduced coordination, judgment impaired (legal limit in most of Europe and Australia); 0.08% — significant motor and cognitive impairment (US/UK driving limit); 0.10% — slurred speech, poor reaction time; 0.15% — major balance and memory impairment; 0.30%+ — risk of unconsciousness; 0.40%+ — life-threatening. Charts are estimates only — actual BAC varies with hydration, food, medication, and individual metabolism. Sources: NIAAA, Widmark (1932), CDC Impaired Driving fact sheet.