Does eating before drinking really help?

Yes — food slows alcohol absorption by delaying gastric emptying, reducing peak BAC by 20–50% and spreading absorption over more time. However, food consumed after drinking does not lower existing BAC.

Why do I feel more drunk on less sleep?

Fatigue independently impairs cognitive function and amplifies alcohol's sedative effects. Sleep deprivation and alcohol both impair the prefrontal cortex, creating a compounding effect even at low BAC.

Is the 0.08% limit the same everywhere?

In the US, 0.08% applies to drivers 21+ in all 50 states. Commercial drivers face a 0.04% limit. Most European countries enforce 0.05%, and some (Sweden, Norway) use 0.02%.

Can I be arrested below 0.08% BAC?

Yes. DUI charges can occur at any BAC if impairment is demonstrated. Some states have per-se laws at lower thresholds for drivers under 21.

Does body weight really matter that much?

Yes. A 120 lb person and a 220 lb person drinking the same number of drinks will have dramatically different BAC — the lighter person may be 80–90% higher. Weight affects the volume of body water in which alcohol distributes.

BAC Calculator — Blood Alcohol Content

How to Use This Calculator

1

Enter Body Details

Set your biological sex, weight, and optionally height and age to unlock the more accurate Watson body water formula.

2

Select Food Factor

Choose Fasted, Light Snack, or Full Meal. Eating before drinking significantly reduces peak BAC by slowing absorption.

3

Log Your Drinks

Use the drink type buttons for common drinks, or enter a custom ABV% and oz for specialty beverages.

4

Plan Your Safety

Use the Sobering Planner tab to check when it's safe to drive or whether you'll be sober when you wake up.

Formula & Methodology

Widmark Formula

BAC = (A × 5.14) / (W × r) − 0.015 × H

A = oz of pure alcohol · W = weight in lbs · r = gender constant · H = hours elapsed. Elimination rate: ~0.015% per hour.

Watson Body Water Formula (optional)

Male TBW = 2.447 − (0.09516 × age) + (0.1074 × height_cm) + (0.3362 × weight_kg)

TBW = total body water. r = TBW / weight_kg. More accurate than fixed gender constants, especially for older adults or athletic builds.

Food Absorption Factor

Peak BAC × food_factor (Fasted=1.0, Snack=0.85, Meal=0.70)

Food slows gastric emptying, reducing peak BAC by 15–30%. Absorption also peaks later: ~45 min fasted vs ~90 min after a full meal.

About this calculation · Accuracy & Methodology

Key Terms

BAC: Blood Alcohol Concentration — the percentage of alcohol in your bloodstream by volume (g/dL × 100).
Standard Drink: A beverage containing 14 grams of pure alcohol: 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%).
Widmark Factor (r): A constant reflecting body water distribution. Male default: 0.73. Female default: 0.66. Watson formula provides personalized values.
Elimination Rate: The liver metabolizes ~0.015% BAC per hour (roughly one standard drink per hour). This rate is largely fixed regardless of body size.
Legal Limit (US): 0.08% BAC for drivers 21+ in all 50 states. Commercial drivers: 0.04%. Under 21: effectively zero tolerance (0.00–0.02% depending on state).

Real-World Examples

Example 1

Dinner Party

180 lb male · 3 glasses wine · full meal · 2.5 hrs

Peak BAC ≈ 0.05% (meal reduces by 30%). Below legal limit. Impairment still present. Sober in ~1.5 hrs.

Example 2

Fasted Night Out

130 lb female · 4 drinks · fasted · 2 hrs

Peak BAC ≈ 0.13%. Significantly over legal limit. Do not drive. Sober in ~7 hrs.

Example 3

Craft Beer Session

200 lb male · 4 IPAs (7.5%) · light snack · 3 hrs

6 standard drinks. Peak BAC ≈ 0.07% (snack reduces absorption). Near legal limit — arrange a ride anyway.

Understanding Blood Alcohol Content

How Your Body Processes Alcohol

Alcohol is absorbed through the stomach (20%) and small intestine (80%), entering the bloodstream within minutes. Food in the stomach slows gastric emptying and reduces the absorption rate, lowering peak BAC significantly. Your liver then metabolizes alcohol at a fixed rate of approximately one standard drink per hour — this rate cannot be meaningfully accelerated.

Why the Rise-and-Fall Curve Matters

Most people think of BAC as only declining after drinking stops. In reality, BAC continues rising for 30–90 minutes after your last drink as alcohol still in your stomach and intestine is absorbed. This is why you can feel more impaired an hour after stopping than you did while drinking. The absorption phase is affected heavily by food — a full meal can extend absorption to 90 minutes and cut peak BAC by 30%.

Why BAC Calculators Are Estimates

Individual BAC varies based on genetics (alcohol dehydrogenase variants), food intake, medications, hydration status, liver health, and even body temperature. This calculator provides estimates based on averaged research values. Actual BAC can differ by 20–40% from the estimate. When in doubt, arrange alternative transportation.

Impairment Begins Below the Legal Limit

Research consistently shows cognitive and motor impairment begins at BAC as low as 0.02%. Reaction time, divided attention, and judgment are measurably degraded well before the 0.08% legal threshold. The legal limit defines when the law presumes impairment, not when driving becomes safe.

BAC Calculator