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California driving lesson · Alcohol, Drugs & DUI

BAC limits & the BAC chart

A 3-minute lesson from the California course. Read the rules and examples, follow the handbook page references, and check your understanding before you move on.

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Read time
3 minutes
Course unit
Alcohol, Drugs & DUI
Checkpoint questions
6
Source pages
79, 90

Your blood alcohol concentration (BAC) measures how much alcohol is in your bloodstream. The legal limit depends on your age and what you drive, but any amount can impair you.

Blood alcohol concentration (BAC)

The amount of alcohol in your blood. A BAC of 0.10% means 0.10 grams of alcohol in 100 milliliters of blood.

Handbook p. 90 ↗

Illegal BAC levels

Illegal BAC levels
DriverIllegal at
21 or older0.08% or higher
Under 210.01% or higher
On DUI probation (any age)0.01% or higher
Vehicle requiring a commercial license0.04% or higher
Driving a passenger for hire0.04% or higher
Handbook p. 79 ↗

Know the rule

Driving with an illegal BAC lets an officer charge you with DUI. Depending on your impairment, you may be arrested and convicted of DUI even without a BAC measurement.

Handbook p. 79 ↗

Know the rule

A BAC below the legal limit does not mean it is safe to drive; almost everyone feels negative effects of alcohol below the limit.

Handbook p. 79 ↗

Estimated BAC by drinks and body weight (male / female)

Estimated BAC by drinks and body weight (male / female)
Drinks100 lb160 lb240 lb
1.06 / .07.04 / .04.02 / .03
2.12 / .13.07 / .08.05 / .06
3.18 / .20.11 / .12.07 / .08
4.24 / .26.15 / .17.10 / .11
5.30 / .33.19 / .21.12 / .14
Handbook p. 79 ↗

Know the rule

On the chart, zero drinks is the only safe driving limit. Even one drink can affect your ability to drive safely.

Handbook p. 79 ↗
1 drink

1.5 oz of 80 proof liquor, 12 oz of 5% beer, or 5 oz of 12% wine

Handbook p. 79 ↗
−0.01% / 40 min

Subtract 0.01% for each 40 minutes that pass between drinks

Handbook p. 79 ↗

Know the rule

Fewer than 5 persons out of 100 will exceed the chart values.

Handbook p. 79 ↗

Know the rule

It is also illegal to drink alcohol or take drugs while operating a boat, jet ski, water skis, aquaplane, or similar vessel.

Handbook p. 79 ↗

Put it into practice

A 19-year-old has one beer and feels fine. At 160 lb the chart estimates about .04% BAC, far above the 0.01% limit for drivers under 21. Driving would be illegal.

Check your understanding

Read the question, decide on an answer, then open it to check the explanation. These are Roadwise study questions based on the source handbook.

What is the illegal BAC limit for a driver 21 years old or older?
  1. 0.05%
  2. 0.10%
  3. 0.08%
  4. 0.04%

Answer: 0.08%

It is illegal to drive with a BAC of 0.08% or higher if you are 21 or older.

Handbook p. 79 ↗
What is the illegal BAC limit for a driver under 21 years old?
  1. 0.08%
  2. 0.05%
  3. 0.00%
  4. 0.01%

Answer: 0.01%

Drivers under 21 may not drive with a BAC of 0.01% or higher, essentially a zero-tolerance rule.

Handbook p. 79 ↗
What is the illegal BAC limit for a driver operating a vehicle that requires a commercial license?
  1. 0.04%
  2. 0.08%
  3. 0.01%
  4. 0.02%

Answer: 0.04%

The illegal BAC limit is 0.04% or higher for drivers of vehicles requiring a commercial license.

Handbook p. 79 ↗
What is the illegal BAC limit for someone driving a passenger for hire?
  1. 0.08%
  2. 0.04%
  3. 0.01%
  4. 0.06%

Answer: 0.04%

Drivers transporting a passenger for hire are held to a 0.04% BAC limit, same as commercial drivers.

Handbook p. 79 ↗
What is the illegal BAC limit for a driver of any age who is on DUI probation?
  1. 0.08%
  2. 0.04%
  3. 0.01%
  4. 0.02%

Answer: 0.01%

A driver on DUI probation is illegal to drive at a BAC of 0.01% or higher, regardless of age.

Handbook p. 79 ↗
Does having a BAC below the legal limit guarantee it is safe to drive?
  1. Yes, below 0.08% it is safe
  2. Yes, as long as you feel fine
  3. No, alcohol affects most people below the limit
  4. Yes, if you wait 40 minutes

Answer: No, alcohol affects most people below the limit

Even below the legal limit, alcohol affects most people's driving ability, so it may not be safe.

Handbook p. 79 ↗
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