BAC Calculator — Blood Alcohol Content

Use the BAC Calculator

Estimate current BAC by entering drinks, %ABV, weight, sex, and hours. This blood alcohol calculator is for education only—not legal advice.

How to Use BAC Calculator — Blood Alcohol Content

1. Step 1: Choose units

   Select Imperial (oz, lb) or Metric (mL, kg) at the top.

2. Step 2: Add your drinks

   Tap quick‑add (beer, wine, shot, cocktail) or add a custom drink with volume and %ABV.

3. Step 3: Enter weight and sex

   Type your body weight and select sex; these affect distribution of alcohol.

4. Step 4: Set time window

   Enter hours since your first drink to estimate current BAC with elimination.

5. Step 5: Review BAC and timing

   See estimated BAC, legal‑limit markers, and time to reach 0.05% and 0.00%.

Key Features

• Mobile‑friendly inputs
• Standard drink presets
• Metric and imperial units
• Widmark formula with burn‑off
• Legal limit markers
• Time‑to‑sober estimate

Understanding Results

BAC Calculator Formula

This tool estimates BAC using a Widmark‑style equation. First we convert each drink into grams of pure alcohol using its volume and %ABV (ethanol density ≈ 0.789 g/mL). We then divide by your estimated body water volume using a sex‑specific distribution factor (r ≈ 0.68 for males, 0.55 for females) and your weight. Finally, we subtract a typical metabolic elimination rate of about 0.015% BAC per hour since your first drink to approximate your current level.

In plain language: more grams of alcohol, lower body water, and less time for metabolism all push BAC higher. Weight and sex matter because alcohol distributes in body water rather than fat tissue. Our blood alcohol calculator turns these factors into a clear estimate you can track.

Interpreting Blood Alcohol Calculator Results

Many regions set a per se legal driving limit of 0.08% BAC, and some use 0.05%. People can experience impairment well below those thresholds. Around 0.02–0.03% some feel mild effects; by 0.05–0.06% reaction time and judgment are often impaired; ≥0.08% is associated with clear deficits in coordination and attention. These are broad generalizations and not advice.

The calculator also estimates time to drop below 0.05% and to 0.00%, assuming average elimination. Because real rates vary, treat the timing as conservative guidance and pad extra time when safety matters.

Assumptions & Limitations

This BAC calculator is for education only. Individual absorption and metabolism differ with genetics, medications, health conditions, sleep, stress, hydration, and whether you ate. The tool cannot determine legal fitness to drive or work. Always choose the safest option—plan a ride, designate a driver, or wait longer than the estimate suggests.

Complete Guide: BAC Calculator — Blood Alcohol Content

Use our BAC calculator to estimate blood alcohol levels from drinks, ABV, weight, sex, and hours. See limit markers, impairment ranges, and time to sober.

The goal of this BAC calculator is awareness. It converts your drinks into grams of alcohol, estimates how that alcohol distributes in your body based on sex and weight, and subtracts a typical amount that your body metabolizes per hour. You get a simple, mobile‑friendly view of your estimated blood alcohol concentration right now, plus a conservative estimate of how long it might take to return below common thresholds.

What is BAC?

BAC stands for blood alcohol concentration. It represents the percentage of alcohol circulating in your blood. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. Laws, safety policies, and health guidance often refer to BAC thresholds because they correlate with changes in reaction time, judgment, and coordination. Importantly, two people can reach different BACs from the same drinks due to differences in body water, genetics, medications, health conditions, and timing.

Most guidance uses standardized drinks to make comparisons easier. In the U.S., one standard drink has about 14 grams of pure alcohol (roughly a 12 oz beer at 5% ABV, 5 oz of wine at 12% ABV, or a 1.5 oz shot of 40% spirits). This lets you estimate BAC more consistently than counting glasses alone, which vary a lot in size and strength.

How the BAC calculator works

Under the hood, this tool uses a Widmark‑style approach. First, it converts each drink to milliliters in your chosen unit system, multiplies by the drink’s alcohol by volume (%ABV), and uses the density of ethanol to get grams of pure alcohol. It then divides by an estimate of your total body water, which depends on your weight and a sex‑specific distribution factor (roughly 0.68 for men and 0.55 for women). Finally, it subtracts an average elimination rate (about 0.015% BAC per hour) from the starting time you provide to estimate your BAC now.

Because biology is variable, there is no single “correct” r value or elimination rate for everyone. Some people metabolize closer to 0.010% BAC per hour and others around 0.020%. Food can slow absorption and lower peak values even when the total alcohol is the same. For those reasons, the BAC number should be read as a useful estimate—never as proof you are fit to drive or work.

If you prefer a broader session view (standard drinks, calories, cost) alongside an approximate BAC, the Alcohol Calculator offers a flexible per‑drink log with quick presets and customization.

Inputs explained

The calculator asks for details that meaningfully change the estimate. Here’s what each one does, and tips for entering practical values.

• Units: Choose Imperial (oz, lb) or Metric (mL, kg). You can switch anytime; presets adapt automatically.
• Drinks: Use quick‑add buttons for common servings or enter a custom drink with volume and %ABV. Quantity is editable so you can adjust without re‑adding.
• Weight: Enter your current body weight. It scales your estimated body water—more body water usually means a lower BAC for the same alcohol dose.
• Sex: Used only to pick the distribution factor (r). It does not imply binary biology; it simply reflects historical parameters used in the Widmark equation.
• Hours since first drink: This controls the subtraction for metabolism. If you started two hours ago, the estimate subtracts ≈0.030% BAC from the starting value.

Want to plan a ride or a safe end time? Pair this tool with our Sobriety Calculator to track milestones, or use the BAC decline table in the app to see how your level may drop over the next few hours assuming no additional drinking.

Legal limits and context

In many U.S. states, 0.08% BAC is the per se limit for non‑commercial adult drivers, and some countries and states use 0.05%. Commercial drivers and young drivers often have stricter limits. Even below these values, impairment can be present. The safest choice is always to plan a ride, designate a driver, or wait longer than you think you need.

Laws and penalties vary by location. For health‑focused guidance on alcohol, check resources from the National Institute on Alcohol Abuse and Alcoholism (NIAAA) and the CDC. Our calculator aims to support planning and awareness, not legal interpretation.

Typical effects by BAC level (approximate)

Everyone’s experience differs, but the following descriptions can help interpret ranges. Use these as broad signposts, not guarantees.

• 0.00–0.02%: Minimal to mild effects for most; subtle relaxation; still best to be cautious with tasks requiring attention.
• 0.03–0.05%: Noticeable effects for many; slows reaction time and divided attention. Some jurisdictions consider 0.05% a per se limit.
• 0.06–0.07%: Impairment typically evident—coordination, tracking, and judgment degrade. Driving is unsafe.
• ≥0.08%: Clear deficits in reaction time, judgment, and motor control. Illegal to drive in many places at or above this level.

Alcohol can also affect sleep quality, heart rate variability, and next‑day alertness. If you’re planning around rest, the Sleep Calculator and Sleep Cycle Calculator can help you set wake times and estimate cycles.

Pacing, food, and hydration

Small choices can lower your peak BAC and improve comfort. Eating beforehand slows absorption and can flatten the peak. Hydrating between drinks won’t lower BAC directly, but it can improve how you feel and reduce next‑day grogginess. Pacing with lower‑ABV options is another effective strategy: swapping a cocktail for a beer or a smaller pour can meaningfully change the curve.

If hydration is a goal, pair this tool with the Hydration Calculator. For nutrition planning, see our Calorie Intake Calculator and Protein Calculator.

Worked examples

These examples are for illustration and use rounded values. Your results may differ due to rounding and biological variability.

Example A (steady evening): Two beers (12 oz, 5% each) over 2 hours for a 160 lb (72.6 kg) female. Pure alcohol ≈ 2 × 14 g = 28 g ⇒ ~2 standard drinks. Starting BAC ≈ (28 ÷ (0.55 × 72600)) × 100 ≈ 0.070%. Subtract ≈0.030% for two hours gives ≈0.040% now. Eating beforehand and spacing the beers could lower the observed peak.

Example B (mixed): One cocktail (8 oz, 15%) + one wine (5 oz, 12%) over 3 hours for a 190 lb (86.2 kg) male. Alcohol ≈ (8 × 29.57 × 0.15 × 0.789) + (148 × 0.12 × 0.789) ≈ 28 g + 14 g = 42 g ⇒ ~3 standard drinks. Starting BAC ≈ (42 ÷ (0.68 × 86200)) × 100 ≈ 0.072%. Subtract ≈0.045% for three hours ≈ 0.027% now.

Example C (shots in a short window): Three 1.5 oz shots at 40% in 1 hour for a 150 lb (68.0 kg) male. Alcohol ≈ 3 × (44 × 0.40 × 0.789) ≈ 41.6 g ⇒ ~3 standard drinks. Starting BAC ≈ (41.6 ÷ (0.68 × 68000)) × 100 ≈ 0.090%. After one hour, subtract ≈0.015% ⇒ ≈ 0.075%. Faster consumption often produces higher peaks for the same total grams.

Common myths about lowering BAC

• Coffee sobers you up: False. It may make you feel more awake but does not change BAC.
• Cold showers or exercise eliminate alcohol faster: False. Only time changes BAC in a meaningful way.
• Food eliminates alcohol already absorbed: False. Food can slow absorption if eaten before or with drinks, but it does not remove alcohol once absorbed.
• You can “feel” your exact BAC: False. Perceived impairment varies widely and is not a precise gauge of your level.

Plan ahead: pacing and safer choices

If you choose to drink, decide your limit before you start and pace at one standard drink per hour or slower. Alternate with water, eat a meal beforehand, and set up transportation that does not depend on your moment‑to‑moment judgment (rideshare, designated driver, public transit). Logging drinks as you go improves accuracy more than trying to reconstruct the night later. The calculator does not save data; screenshots are a simple way to keep a personal note.

Remember that estimation cannot account for health conditions, medications, or unusual responses. If safety is on the line, the only reliable option is to not drive and to give yourself substantially more time than the estimate suggests. When in doubt, choose the conservative path.

Useful related tools

• Alcohol Calculator — plan sessions with per‑drink logging, calories, and cost.
• Alcohol Units Calculator — track weekly intake in UK units and limits.
• Sobriety Calculator — mark milestones and support personal goals.
• Hydration Calculator — pace water intake alongside drinks.
• Sleep Calculator — set wake times and plan recovery.
• Liver Function Calculator — understand lab ranges with context.

Limitations and safety notes

This BAC calculator is informational only. It does not provide medical advice and cannot determine legal fitness to drive or perform any safety‑sensitive task. Absorption and elimination vary with genetics, medications, health conditions, gastric emptying, stress, sleep, and hydration. For the same drinks, two people can have different BACs and feel different levels of impairment.

Use the estimates conservatively. If safety is involved, choose the most cautious option—plan a ride, use a designated driver, or wait substantially longer than the tool suggests. If you have questions about alcohol and health, talk with a qualified clinician. If you’re exploring changes to your relationship with alcohol, small steps—like logging drinks, setting limits, and planning dry days—can help.

References

• Centers for Disease Control and Prevention (CDC).CDC: Alcohol
• National Institute on Alcohol Abuse and Alcoholism (NIAAA). Alcohol and your health resources.

Frequently Asked Questions