Blood Alcohol Calculator (BAC)
Estimate blood alcohol concentration from body weight, elapsed time, and mixed beer, wine, liquor, or custom drink entries with editable serving sizes and ABV.
Estimate BAC from body weight, elapsed time, serving size, and ABV.
BAC calculator inputs
Estimated result
- Approximate time to 0.00%
- 1 hr 38 min
- Impairment range
- 0.020 to 0.049 g/dL
- U.S. standard drinks
- 1.86
- Pure alcohol
- 26.04 g
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What does the Blood Alcohol Calculator (BAC) calculate?
The Blood Alcohol Calculator (BAC) converts the values you enter into a structured estimate using the formulas and assumptions documented on this page. Use the result to compare scenarios, review the calculation details, and identify sensitive inputs. Check the guide and formula sections before using the estimate for an important decision.
Blood Alcohol Calculator at a Glance
- Estimates BAC from entered body weight, elapsed time, serving size, quantity, and ABV.
- Combines beer, wine, liquor, and a custom drink in one calculation.
- Normalizes U.S., U.K., and metric weight and volume units before calculating.
- Shows pure alcohol, U.S. standard drinks, current estimated BAC, and a time projection.
- Provides an estimate only. It cannot determine sobriety or whether driving is safe or legal.
History of BAC Estimation
Blood alcohol concentration is measured from a biological sample, but mathematical models are also used to estimate how a known amount of alcohol may distribute through the body. Widmark-style equations became a common starting point for these estimates.
Modern forensic guidance emphasizes uncertainty. A distribution ratio, elimination rate, and drinking history are estimates, so a calculated BAC must not be treated as the equivalent of a breath or blood test.
What This BAC Calculator Does
The calculator converts each entered serving into milliliters, multiplies its volume by ABV and ethanol density, and adds the resulting grams of pure alcohol. It then applies a forward Widmark-style equation and subtracts the modeled decline over the time entered.
The result includes estimated BAC in g/dL, estimated BAC before the elapsed-time deduction, U.S. standard drinks, drink-by-drink alcohol amounts, an impairment range, and a past-to-projected time chart with a text alternative.
Who Should Use It
This educational tool is for adults who want to understand how drink quantity, serving size, ABV, body weight, and elapsed time affect a population estimate. It can also help students reproduce the arithmetic behind standard-drink and BAC examples. Review the BAC Calculator assumptions before relying on this result for decisions.
It is not designed for children, pregnancy guidance, clinical care, legal evidence, retrograde extrapolation, alcohol dosing, or decisions about driving.
Problems It Solves
- Separates container size from alcohol strength.
- Combines different drink types without assuming every serving is identical.
- Converts pounds, kilograms, grams, milliliters, liters, U.S. and U.K. fluid ounces, cups, pints, shots, cans, and bottles.
- Shows when a large or strong pour represents more than one U.S. standard drink.
- Makes the equation constants and uncertainty visible.
Key Benefits
The same tested Decimal.js engine powers the page, examples, embed, and PDF. Every drink input remains editable, preset values are documented, and calculations retain decimal precision until values are formatted for display.
BAC Definitions
- BAC
- Blood alcohol concentration, commonly expressed here as grams of alcohol per deciliter of blood.
- ABV
- Alcohol by volume, the percentage of a beverage's volume that is alcohol.
- U.S. standard drink
- A serving containing about 14 grams, or 0.6 U.S. fluid ounces, of pure alcohol.
- Distribution ratio
- A population parameter used to estimate how alcohol distributes through body water.
- Elimination rate
- The modeled decline in BAC per hour. Individual rates vary.
- Time to zero
- The mathematical time for this model to reach approximately 0.000 g/dL, not a safe-driving countdown.
When to Use It
Use the calculator after identifying the actual size and labeled ABV of each drink, when checking whether a pour contains one or several standard drinks, or when learning how a BAC estimate changes with weight and elapsed time. If there is any question about driving, use a sober driver or another safe ride instead of relying on a calculation.
How the Calculation Works
For “How the Calculation Works,” the BAC Calculator organizes the relevant inputs, applies the documented method, and shows a result that can be compared across scenarios. The points below identify the specific considerations and assumptions users should review before relying on the estimate.
- Validate and normalize body weight and every serving volume.
- Calculate pure alcohol grams for each drink and add them.
- Apply the selected distribution ratio to the weight in grams.
- Subtract the elimination-rate assumption multiplied by elapsed hours.
- Keep the estimate at or above zero and build the time projection.
Review each variable on the BAC formula page or reproduce three scenarios on the BAC examples page.
Frequently Asked Questions
What is BAC?
Blood alcohol concentration (BAC) is the amount of alcohol in a person's bloodstream, commonly expressed as grams of alcohol per deciliter of blood. For a useful BAC Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
How accurate is an online BAC calculator?
It is a population estimate, not a measurement. Food, drinking pace, body composition, health, medicines, absorption, and individual metabolism can make actual BAC higher or lower. Use realistic inputs and review the BAC Calculator assumptions before relying on this result for decisions.
What counts as one U.S. standard drink?
In the United States, one standard drink contains about 14 grams, or 0.6 fluid ounces, of pure alcohol. Container size alone does not determine the number of standard drinks. Review the BAC Calculator assumptions before relying on this result for decisions.
Can I use this result to decide whether to drive?
No. Do not use an estimated BAC to decide whether to drive. Alcohol can impair driving below common legal thresholds, and only time reduces the alcohol in the body. Review the BAC Calculator assumptions before relying on this result for decisions.
Why are the formula assumptions shown?
Widmark distribution and elimination values vary among people and studies. Showing the assumptions makes the estimate and its uncertainty visible instead of hiding them. Use realistic inputs and review the BAC Calculator assumptions before relying on this result for decisions.
How do I enter a cocktail or custom pour?
Use the fixed Other row, choose Custom volume, enter the volume of one serving and its supported unit, then enter the labeled or recipe-based ABV. Use realistic inputs and review the BAC Calculator assumptions before relying on this result for decisions.
One Useful BAC Fact
A 12 U.S. fl oz beer at 5% ABV, 5 U.S. fl oz wine at 12% ABV, and 1.5 U.S. fl oz spirit at 40% ABV each contain about the same amount of pure alcohol. Larger pours and higher ABV change that comparison.
Conclusion
A BAC calculator is most useful for understanding inputs and uncertainty. It is not a sobriety test. Real absorption, metabolism, health, medicines, food, and drinking pace can produce a materially different BAC.