Commercial Driver’s License (CDL) · Knowledge Test Overview
Question and Passing Score Overview
On this page 6 sections
In 30 seconds
The CDL knowledge tests share one pattern: nearly every test requires 80 percent to pass, and only the number of questions changes. General Knowledge is 50 with 40 to pass, Hazmat is 30 with 24, Air Brakes is 25 with 20, and Combination, Tank, Passenger, and School Bus are each 20 with 16. Doubles/Triples is the exception, with a count and score that vary by state.
Why this matters
Knowing the size and passing score of every CDL knowledge test before you walk in lets you plan which tests to bundle into one visit, how many misses you can afford on each, and where a single wrong answer carries the most weight.
The college version
In normal terms
- Learn one number, 80 percent, then remember how long each test is.
- Shorter tests cost more per miss: four on a 20-question test, ten on General Knowledge.
- Bundle the tests your class needs into one visit; leave uncertain endorsements for later.
- Doubles/Triples is the only test where you must check your state's CDL manual for the count.
Concepts in this outline
- General Knowledge: 50 questions; 40 (80%) — The longest test and the only one required for every class; ten misses are allowed.
- Air Brakes: 25 questions; 20 (80%) — Five misses allowed; number-heavy questions make it the least forgiving of fuzzy memory.
- Combination Vehicles: 20 questions; 16 (80%) — Class A only; four misses allowed on a narrow, one-chapter test.
- Hazardous Materials (H): 30 questions; 24 (80%) — The largest endorsement test, with six misses allowed and a TSA check required before issuance.
- Tank Vehicles (N): 20 questions; 16 (80%) — Four misses allowed; pairs with H to produce the X endorsement.
- Passenger Transport (P): 20 questions; 16 (80%) — Four misses allowed; required for vehicles designed for 16 or more people.
- School Bus (S): 20 questions; 16 (80%) — Four misses allowed; stacks on top of the P endorsement.
- Doubles/Triples (T): questions vary; passing score varies — The one test where the count and score are set by each state and listed in your state's CDL manual.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Think of a teacher who gives quizzes of different lengths. Some have 20 words, some have 50, but you always need 8 of every 10 right. CDL knowledge tests work that way. Look at the passing scores. Forty of 50, 24 of 30, 20 of 25, 16 of 20. Every one is 80 percent. That one number is the standard for every fixed-length CDL knowledge test. Remember the standard and each test's length, and the passing score is simple math.
The lengths sort into four groups. General Knowledge is the long one at 50 questions. Hazardous Materials is next at 30, because hazmat has the most rules. Air Brakes is 25. A whole group sits at 20: Combination Vehicles, Tank Vehicles, Passenger Transport, and School Bus. The odd one out is Doubles/Triples, where the count and passing score vary because each state sets its own. Your state's CDL manual gives the real number.
The 80 percent rule feels different on each length. On General Knowledge you may miss ten questions, a nice cushion. On Air Brakes you may miss five. On any 20-question test you may miss only four. The shortest quizzes deserve the most careful reading. Air Brakes is full of numbers, and it punishes a fuzzy memory of psi values most of all. Psi is a way to measure how hard air is pushing.
The table also helps you plan a visit. A Class B applicant needs General Knowledge and, for almost any real truck, Air Brakes. That is 75 questions in one sitting. A Class A applicant adds Combination, for 95. Endorsement tests stack on top and do not depend on each other. Tank plus hazmat adds 50 more. Most drivers take their core tests in one morning and add endorsements the same day or later. Every test is scored on its own, so a fail on one does not erase a pass on another. You come back only for the test you missed.
The way the quizzes are given stays the same too. In most states the tests are multiple choice on a computer, scored right away. The questions come from the same federal manual every state uses. What changes by state, besides the T count, is the retake policy. That means the waiting period, the attempts allowed, and the fee per try. None of that changes the 80 percent rule or the fixed question counts.
So hold onto the teacher's rule. The quizzes are 20, 25, 30, and 50 questions long. The grade to pass is always 80 percent. Doubles/Triples is the quiz you measure when you get there.
Worked example
Keisha Alvarado is going for a Class A with tank and hazmat endorsements to drive for a chemical carrier. Before scheduling, she writes the table out by hand: General Knowledge 50 and 40, Air Brakes 25 and 20, Combination 20 and 16, Tank 20 and 16, Hazmat 30 and 24. She notices every passing score is 80 percent and stops trying to memorize five separate numbers.
She books one morning for the three core tests, 95 questions total, and passes all three: 45 of 50, 21 of 25, and 17 of 20. Two weeks later, with her TSA fingerprints in, she returns for Tank and Hazmat and scores 18 of 20 and 25 of 30. She never needed Doubles/Triples, so she never had to look up her state's varying count. Her plan came straight from the table.
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