Transparent method
The formula
Widmark: BAC % = alcohol grams ÷ (body weight (g) × r) × 100 − (hours × 0.015)
Worked example
Estimated blood alcohol concentration0.055%
Estimated hours until 0.00%3.7
Example inputs
Standard drinks3
Weight160
SexMale
Hours since first drink2
How to interpret the result
Never use this to judge whether it is safe to drive. Individual metabolism varies and the estimate can be wrong in either direction. This is a formula-based estimate; individual results vary with factors the formula does not measure.
Sensitivity evidence
How standard drinks changes the estimated blood alcohol concentration
| Standard drinks | Estimated blood alcohol concentration | Estimated hours until 0.00% |
|---|---|---|
| 1 | 0.000% | 0 |
| 2 | 0.027% | 1.8 |
| 3worked example | 0.055% | 3.7 |
| 4 | 0.083% | 5.6 |
| 5 | 0.112% | 7.5 |
Every input, tested
Which input moves the estimated blood alcohol concentration most
| Input | Tested from | To | Estimated blood alcohol concentration at each end | Swing |
|---|---|---|---|---|
| Standard drinks | 2 | 4 | 0.027% to 0.083% | 0.057% (103%) |
| Sex | Male | Female | 0.055% to 0.075% | 0.020% (37%) |
| Weight | 144 | 176 | 0.065% to 0.047% | 0.017% (31%) |
| Hours since first drink | 1.8 | 2.2 | 0.058% to 0.052% | 0.006% (11%) |
Two variables at once
Estimated blood alcohol concentration by standard drinks and weight
| Standard drinks \ Weight | 128 | 160 | 192 |
|---|---|---|---|
| 1 | 0.005% | 0.000% | 0.000% |
| 2 | 0.041% | 0.027% | 0.017% |
| 3 | 0.076% | 0.055% | 0.041% |
| 4 | 0.112% | 0.083% | 0.065% |
| 5 | 0.147% | 0.112% | 0.088% |
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Standard drinks | 3 | Number of standard (14g alcohol) drinks. |
| Weight | 160 | Body weight in pounds. |
| Sex | Male | Widmark's distribution ratio r differs by sex. |
| Hours since first drink | 2 | Elapsed time since the first drink. |
| Estimated blood alcohol concentration | 0.055% | |
| Estimated hours until 0.00% | 3.7 | |
Inputs, definitions and assumptions
Standard drinks
Number of standard (14g alcohol) drinks.
Weight
Body weight in pounds.
Sex
Widmark's distribution ratio r differs by sex.
Hours since first drink
Elapsed time since the first drink.
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