Formula and calculation method
Estimated BAC (%) = max(0, ethanol grams / [body mass grams × distribution factor] × 100 − elimination × hours).
Absorption, food, physiology, medications and timing make this highly uncertain. Never use an estimated BAC to decide whether driving or another safety-critical activity is safe.
How to use bac calculator
- Set Measurement system by choosing the option that matches your calculation.
- Set Weight (kg or lb). The example below uses 70.
- Set Pure ethanol consumed (grams). The example below uses 28.
- Set Hours since drinking began. The example below uses 2.
- Set Widmark distribution factor. The example below uses 0.68.
- Set Elimination (% BAC per hour). The example below uses 0.015.
- Select Calculate to update the result. Reset restores the illustrated inputs. Copy, print or download your own result if you need a record.
Worked example
Example inputs
- Measurement system
- Metric (kg, cm)
- Weight (kg or lb)
- 70
- Pure ethanol consumed (grams)
- 28
- Hours since drinking began
- 2
- Widmark distribution factor
- 0.68
- Elimination (% BAC per hour)
- 0.015
- Illustrative BAC estimate (%)
- 0.02882353
Factors affecting your result
Absorption, food, physiology, medications and timing make this highly uncertain. Never use an estimated BAC to decide whether driving or another safety-critical activity is safe.
Changing measurement system changes the scenario being evaluated. Adjust one input at a time when comparing results, keep a copy of the assumptions, and compare values using the same unit and period. A precise arithmetic result does not make an uncertain assumption precise.
Frequently asked questions
How does the bac calculator work?
Estimated BAC (%) = max(0, ethanol grams / [body mass grams × distribution factor] × 100 − elimination × hours).
What inputs does BAC Calculator need?
Enter measurement system, weight (kg or lb), pure ethanol consumed (grams), hours since drinking began, widmark distribution factor, elimination (% bac per hour). Read the unit labels; percentages are entered as ordinary percentages, not decimal fractions.
How should I interpret the bac calculator result?
Absorption, food, physiology, medications and timing make this highly uncertain. Never use an estimated BAC to decide whether driving or another safety-critical activity is safe.
Are my bac calculator inputs uploaded?
No. The calculation runs in this browser. Favorites, recent tool names, theme and formatting preferences may be saved locally, but calculation inputs are not sent to a calculation server or stored by this website. Shared links do not include entered values.
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