Blood Alcohol Content Calculator
Enter your body weight, biological sex, what you drank and how long ago you started, and the calculator returns an estimated blood alcohol content using the Widmark formula. It’s a useful gut-check for whether to order a car home — not a legal breathalyzer. Actual BAC depends on food in your stomach, medication, metabolism and hydration, and can differ from the estimate by 20% or more.
How BAC is estimated
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1
Enter your weight and sex
Widmark uses a distribution ratio r (0.68 for men, 0.55 for women on average). Sex at birth, not identity, drives the physiology here.
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2
Log each drink
Add drinks by type (beer, wine, spirits) and volume. The tool converts to grams of pure ethanol using standard ABV.
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3
Enter elapsed time
Hours since your first drink. Alcohol metabolises at about 0.015 BAC per hour for most adults.
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4
Read the estimate
Current BAC, peak BAC, and estimated time until you drop below 0.05 and 0.00. A coloured impairment band shows relative risk.
Widmark formula
BAC (%) = (A × 5.14 / (W × r)) − 0.015 × H
Where:
- A = alcohol consumed in ounces (or grams; the constant changes)
- W = body weight in pounds (or kg)
- r = distribution ratio (0.68 male, 0.55 female)
- H = hours since first drink
One US standard drink = 0.6 fl oz (14 g) of pure ethanol, which is roughly:
| Beverage | Serving | ABV |
|---|---|---|
| Regular beer | 12 fl oz | ~5% |
| Craft / strong beer | 12 fl oz | ~7-9% |
| Table wine | 5 fl oz | ~12% |
| Fortified wine | 3 fl oz | ~17% |
| 80-proof spirits | 1.5 fl oz | 40% |
Impairment at common BAC levels
- 0.02 — relaxation, slight warmth, mild judgement changes
- 0.05 — reduced coordination; legal limit in many European countries
- 0.08 — significant impairment; US and UK (England/Wales) legal driving limit
- 0.10 — slurred speech, poor muscle control
- 0.15 — major impairment, blackout risk
- 0.30+ — stupor, medical emergency territory
Why the estimate can be wrong
- Food slows absorption by up to 50%. The formula assumes fasted drinking.
- Body composition: higher fat percentage lowers the distribution volume and raises BAC for the same dose.
- Medication and illness alter metabolism significantly.
- Chronic drinkers process ethanol faster (up to 0.02 BAC/hour).
If you are deciding whether to drive, do not use this calculator to decide. Use a breathalyzer, a rideshare, or do not drive.
Frequently Asked Questions
No. Law enforcement measures BAC with calibrated breathalyzers or blood draws. The Widmark estimate is educational and can differ materially from an actual test result.
Roughly 0.015 per hour for a typical adult — about one standard drink burned off per hour. Coffee, cold showers and water do not speed this up.
Women tend to have a lower total body water percentage and less gastric alcohol dehydrogenase, leading to higher peak BAC from the same dose. Widmark encodes this with different r values.
Absolutely not. Only a calibrated breath or blood test produces a legally defensible reading. Treat the estimate as a rough planning tool, never as evidence.
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