BAC Calculator

Widmark Formula Estimate

This is a rough estimate only — not a breathalyzer substitute — and must never be used to judge your fitness to drive. If you have consumed any alcohol, do not drive.

Enter your details to see a rough, informational BAC estimate using the Widmark formula.

Parameters

Sex

Male Female

Weight (kg)

Weight (lbs)

Standard Drinks

Hours Elapsed

Estimated BAC

% blood alcohol concentration

Enter your details to see your estimate.

Validation Error

Please provide a valid weight, drink count, and hours elapsed to proceed.

Understanding the Widmark BAC Formula

The Widmark formula is a decades-old approximation used to estimate blood alcohol concentration from body weight, sex, drinks consumed, and time elapsed. It is a rough population-average model, not a precise individual measurement.

What Counts as a Standard Drink

In the US, a standard drink is about 14 grams of pure alcohol — roughly a 12oz beer, a 5oz glass of wine, or a 1.5oz shot of spirits.

Body Water Distribution

The formula uses a different distribution ratio for men (0.68) and women (0.55), reflecting average differences in body water content.

Elimination Over Time

The body eliminates alcohol at roughly 0.015% BAC per hour — the formula subtracts this based on time elapsed since drinking began.

Massive Individual Variation

Food intake, medications, liver function, and genetics all cause real BAC to differ substantially from this formula's output.

The Widmark Formula

\[ BAC = \frac{A}{W \times r} \times 100 - (0.015 \times T) \]

Where A is grams of alcohol consumed, W is body weight in grams, r is the sex-specific distribution ratio, and T is hours elapsed since drinking began.

Critical Safety Notice

This calculator provides a rough, informational estimate only. It is not a breathalyzer substitute and must never be used to judge your fitness to drive, operate machinery, or make any safety-critical decision.

Real BAC is affected by factors this formula cannot measure — food intake, medications, individual metabolism, and more. If you have consumed any alcohol, do not drive. Use a certified breathalyzer, or better, arrange alternate transportation.

Important Limitations

Population average, not individual measurement: Only a breathalyzer or blood test gives an actual, legally reliable BAC reading.
Doesn't account for food, medications, or tolerance: These significantly affect real absorption and impairment.
Impairment isn't purely about the number: Reaction time and judgment can be affected well below common legal BAC thresholds.

Key Takeaways

The Widmark formula is a rough approximation. It was developed decades ago as a population-average model, not a precise individual tool.
Many real-world factors aren't captured. Food, medications, and individual metabolism all shift actual BAC from this estimate.
Impairment can occur below the legal limit. Reaction time and judgment are affected at BAC levels well under common legal thresholds.
This is a rough estimate only — not a breathalyzer substitute — and must never be used to judge your fitness to drive. BAC is affected by factors this calculator cannot measure (food, medications, individual metabolism); if you have consumed any alcohol, do not drive — use a certified breathalyzer or, better, arrange alternate transportation.

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