Widmark Formula
Definition
A = r × W × C, where A is total alcohol in body (g), W is body weight (kg), C is BAC (g per kg), and r is the Widmark factor (about 0.68 for men, 0.55 for women). Used for back-calculation of dose or BAC at time of incident.
- Formula
- A = r x W x C
- A
- Total alcohol in the body (grams)
- W and C
- Body weight (kg) and BAC (g/kg)
- Use
- Back-calculation of dose or BAC at time of incident
Common questions
What assumption does the Widmark formula rely on that limits its accuracy?+
It assumes ethanol distributes uniformly and instantly through body water and that elimination proceeds at a constant zero-order rate, assumptions that do not always hold precisely for a given individual, drinking pattern, or absorption phase.
How is the Widmark formula extended to estimate BAC at an earlier time, such as the time of a road accident?+
Analysts add a back-extrapolation term using an assumed or measured elimination rate per hour to the measured BAC at testing time, though this back-calculation carries additional uncertainty from individual variation in elimination rate and whether absorption was complete.
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