Alcohol Units Guide: Standard Drink Sizes, Weekly Limits & BAC Estimation
One UK unit = 10ml pure alcohol. One US standard drink = 14g pure alcohol. BAC ≈ (drinks × 5.14 / body weight lbs × r) − 0.015 × hours. Learn what moderate drinking really means.
What Is a Standard Drink?
A 'standard drink' is a unit of measurement defining a fixed amount of pure ethanol, regardless of beverage type or serving size. The definition varies by country: United States (NIAAA): 14 grams of pure alcohol = approximately 1.5 oz (44ml) of 80-proof spirits, 5 oz (148ml) of wine at ~12% ABV, or 12 oz (355ml) of regular beer at ~5% ABV. United K
Estimating Blood Alcohol Content (BAC)
The Widmark formula provides an approximation of BAC. r is the Widmark factor representing the fraction of body mass in which alcohol distributes (water-based tissues): 0.73 for men, 0.66 for women (women have more fatty tissue and less total body water per unit weight). Example: 160 lb man drinks 3 beers over 2 hours. BAC = (3 × 5.14) / (160 × 0.7
Evidence-Based Drinking Guidelines
The 2020–2025 US Dietary Guidelines recommend: up to 1 drink/day for women, up to 2 drinks/day for men. Less is better from a health standpoint — the guidelines explicitly state this is not a recommendation to drink. The UK NHS recommends: no more than 14 units per week for both sexes, spread over 3+ days (not saving the week's allowance for one ni
How Alcohol Is Metabolized
The liver metabolizes approximately 1 standard drink (14g ethanol) per hour — equivalent to a BAC decrease of about 0.015% per hour. This rate is relatively constant and cannot be meaningfully accelerated by coffee, exercise, water, or food consumed after drinking. Alcohol dehydrogenase (ADH) in the liver converts ethanol to acetaldehyde, a toxic c
Frequently Asked Questions
How many glasses of wine per week is considered safe?
The Dietary Guidelines (2020–2025) define 'moderate' consumption as up to 1 drink/day for women (5 oz wine per day maximum). Emerging research, including a 2018 Lancet meta-analysis of 700+ studies, found that the safest level of drinking for overall health is zero — any amount i
How long does alcohol stay in your system?
BAC returns to 0 at the rate of approximately 0.015% per hour after drinking stops. A person at BAC 0.15 needs about 10 hours to fully metabolize the alcohol. Breath and blood tests detect alcohol for 12–24 hours. Urine tests can detect ethyl glucuronide (ETG, an alcohol metaboli
Does eating food while drinking reduce BAC?
Food significantly slows alcohol absorption by delaying gastric emptying — alcohol is absorbed primarily in the small intestine. Food eaten before or during drinking can reduce peak BAC by 30–50% compared to drinking on an empty stomach. However, food does not increase the rate o
What is the difference between alcohol tolerance and alcohol dependence?
Tolerance is the adaptation of the nervous system requiring more alcohol to achieve the same effect — a normal physiological response to regular drinking. Dependence (alcohol use disorder) is characterized by loss of control, continued use despite harms, withdrawal symptoms when
Can you build a tolerance to alcohol faster than others?
Genetic factors strongly influence alcohol metabolism rate, tolerance development, and dependence risk. Variations in ADH1B and ALDH2 genes affect how quickly ethanol and acetaldehyde are processed. About 50% of the risk for alcohol use disorder is genetic. People with a family h