Reading BAC Charts Without Treating Estimates as Permission
Key Takeaways
The official chart uses standard drinks consumed over elapsed drinking time and separate male/female weight tables.
Convert container volume and ABV into standard drinks before choosing a chart column.
Chart values are estimates; food, physiology, timing and other substances affect actual risk.
A low estimate or a displayed .00 does not prove sobriety or authorize further service.
What a BAC Chart Does
Appendix E of the official SIR manual contains charts for estimating blood alcohol concentration. They illustrate how drink quantity, elapsed time, body weight and the chart’s male/female categories change an estimate. The charts are teaching tools, not measurements of the person standing in front of a server.
A measured BAC comes from an appropriate test; a chart uses assumptions and broad categories. The official manual warns that actual BAC may differ and that other factors affect impairment. Staff must continue observing speech, appearance, mood, coordination, inhibition and judgment. An estimate does not override the prohibition on serving a person who is intoxicated or showing signs of intoxication.
Prepare the Inputs
First determine the total standard drinks, including known consumption before arrival. One glass is not necessarily one standard drink. A 473 mL beer at 7% contains approximately 473 × 0.07 ÷ 17.05 = 1.94 Canadian standard drinks. Counting it as one would understate the alcohol input.
Next determine elapsed time from when drinking began to the assessment time. Starting at 7 pm and assessing at 9 pm is two hours, not one hour because the last order came at 8 pm. A new venue or a new server does not reset that interval or erase earlier consumption.
Then identify the weight row and the appropriate chart table for the exercise. The official chart labels its tables male and female; those broad physiological categories cannot capture every person’s body composition or individual metabolism. Do not guess a stranger’s precise physiology or present a chart calculation as a diagnosis.
The chart covers specified weights, one to five standard drinks and one to four hours. A scenario outside those inputs cannot be solved reliably by pretending that the final column represents any higher intake. Use the chart as published and identify the limitation.
Follow the Row and Column
The table groups columns by elapsed time. Within each time group, choose the number of standard drinks. Read across the weight row to their intersection. For example, using the official male table, the 200 lb row intersects three drinks over one hour at .04, meaning approximately 0.04% BAC.
Use the decimal carefully. A displayed .04 is four-hundredths of one percent in this chart, not 4% BAC. It corresponds to approximately 40 mg of alcohol in 100 mL of blood. This unit conversion explains the relationship to driving thresholds; it does not show the person’s real measured value.
Original Worked Examples
| Chart exercise | Lookup | Official estimated BAC |
|---|---|---|
| Male, 200 lb, three standard drinks over one hour | Male → 200 lb → 1 Hour → 3 Drinks | .04 |
| Male, 200 lb, four standard drinks over one hour | Male → 200 lb → 1 Hour → 4 Drinks | .07 |
| Female, 140 lb, three standard drinks over one hour | Female → 140 lb → 1 Hour → 3 Drinks | .09 |
| Male, 120 lb, three standard drinks over four hours | Male → 120 lb → 4 Hours → 3 Drinks | .03 |
The first two rows show the effect of adding a standard drink with the other chart inputs fixed. The third shows that using the wrong table or weight can change the result substantially. The fourth shows how elapsed time changes the chart’s estimate, but it does not establish a personal safe-drinking schedule.
Recheck the inputs before the arithmetic. Four cocktails each containing two standard drinks total eight, not four. Eight lies outside the chart’s displayed drink range; choosing the four-drink column because four glasses were served would be a serious error.
Why Actual Risk Can Differ
Drink strength, pour size, earlier consumption and start time may be uncertain. Food can slow absorption. Body composition, age and other individual factors influence response. Drugs may increase impairment without increasing the alcohol number in the same proportion.
BAC may still rise after drinking stops as alcohol is absorbed. A patron who seems stable at the last order may worsen while waiting for transportation. Neither coffee nor water accelerates elimination. Avoid a precise countdown to sobriety based on a broad chart or a typical hourly processing estimate.
The official chart includes cells rounded to .00. That is not proof that a person has no alcohol in their body or can safely drive. Rounding, incomplete inputs and individual variation remain relevant. A server should never promise a guest that a chart proves legal driving ability.
Use the Estimate as a Warning Tool
Driving rules differ from the liquor-service assessment. Federal offences include impairment to any degree and the statutory BAC threshold; BC also has provincial roadside restrictions. A value below a numerical threshold is not a service permit, and other substances or driver-specific restrictions may matter.
Suppose a worksheet gives .04 but the patron is stumbling and slurring. Discontinue service and arrange help based on the observations; do not serve because the chart is below .05. Conversely, staff should not wait for obvious physical collapse when known intake and changing judgment already raise concerns. Chart practice should improve recognition of uncertainty and risk, rather than replace professional monitoring.
Sources checked October 9, 2026
Official SIR manual, July 2026; BC Liquor Control and Licensing Act.
Using the official male chart, what is the estimate for 200 lb and four standard drinks over one hour?
A guaranteed measured .04
Exactly .80
Approximately .07
Approximately .00
Four cocktails contain two standard drinks each. Which input represents the alcohol?
Four drinks because four glasses were used
Eight standard drinks, outside the displayed one-to-five range
Two drinks because each glass contains two
One drink because they were on one bill
The chart gives a low estimate but a patron is stumbling and slurring. What applies?
Wait for a measured .08
Use the estimate as permission to serve
Act on the signs and discontinue liquor service
Offer a double to confirm the estimate
Sections you finish are checked off in the contents.