What are the main air brake numbers on the CDL test?

The common ones are the safety valve at about 150 psi, governor cut-out at 125 to 135 psi, cut-in at 100 to 110 psi, the low air warning at 55 to 60 psi, and spring brakes coming on at about 20 to 45 psi. Confirm the ranges in your state's CDL manual.

What is the difference between cut-in and cut-out?

Cut-out is the higher pressure where the compressor stops pumping. Cut-in is the lower pressure where it starts pumping again.

What does L.A.B. stand for in the air brake check?

L is Leaks (the static check), A is Alarm (the low air warning), and B is Button (the emergency pop-out). It is a memory aid for the in-cab check order.

How often should I review the air brake numbers?

Review them one day after you learn them, again at day 3, and again at day 7. Keep each review to five to ten minutes and write the numbers from memory before you check.

Do I need to know the exact numbers or just the ranges?

Learn the ranges your state's manual gives, because the test can ask for them exactly. Also learn what happens at each level, since questions often ask about the result.

How to Remember Air Brake Numbers for the CDL Test

Do not try to memorize the air brake numbers as one long block. Put five numbers on one card, write them from memory, and review them on day 1, day 3 and day 7. By the end of this post you will have the card, the calendar and a rule for what to do when you miss a number.

Copy this number card and review calendar

Write this on an index card, high to low. The ranges come from CDL Study Buddy's air brakes guide:

Number	What happens there
About 150 psi	Safety valve opens. This means something is wrong.
125 to 135 psi	Governor cut-out. The compressor stops pumping.
100 to 110 psi	Governor cut-in. The compressor starts pumping again.
55 to 60 psi	Low air warning. The buzzer and light come on.
20 to 45 psi	Spring brakes come on by themselves.

After that, set three reminders:

Day 1: write all five numbers from memory.
Day 3: write them again.
Day 7: write them once more, then take a timed Air Brakes practice test.

The exact ranges can differ a little from manual to manual. Check the air brakes section of your own state's CDL handbook. California's section 5 is one example of what that text looks like.

Read the card as a line, not as five facts

A list of five unrelated numbers is hard to hold. A line is easier. Go from the biggest number down: 150, then 125 to 135, then 100 to 110, then 55 to 60, then 20 to 45. Say it out loud twice.

If you want a shorter anchor, many students keep the rounded pump and warning numbers in one phrase: 100, 125, 60. Cut-in is 100, cut-out is 125, the warning is 60. Spring brakes are the 20 to 45 range.

The two that get swapped most are cut-in and cut-out. Use this line: the pump stops at the high number and starts again at the lower one.

Tie every number to what it does

A number you can explain is a number you can pick out of four answers that look close. Learn the pairs:

Cut-out (high): the compressor stops.
Cut-in (lower): the compressor starts again.
Low air warning: you hear a buzzer and see a light. Stop and fix it.
Spring brake range: below this level the spring brakes can come on by themselves, and the vehicle stops whether you want it to or not.
Safety valve: if it opens, something is wrong with the system.

Test questions often ask what happens at a level, not only what the level is. If you only know the number, a question about the result can still trip you up.

Drill the numbers on their own, then mix

Air brakes feels like too many numbers because parts, numbers and inspection steps get mixed together. Kaplan CertPrep suggests drilling those three groups separately and then combining them in full practice tests. Do the same:

Pile	What goes in it	Format
Parts	Compressor, governor, air tanks, spring brakes	A drawing you can redo from memory
Numbers	The five-number card	Recall on days 1, 3 and 7
Check	The in-cab inspection order	Say it out loud in order

For the check, a common memory aid is L.A.B.: Leaks (the static check), Alarm (the low air warning), Button (the emergency pop-out), as CDL Study Buddy lays it out.

When the numbers feel jumbled, stop taking mixed quizzes. Drill only the PSI questions until you stop missing them, then go back to mixed tests.

Review by recalling, not by re-reading

Re-reading feels good because the page looks familiar. It does not prove you can pull the number out on test day. Spaced review guides recommend a first review one day after you learn something, then at three days, then at a week, and they keep each session short and based on recall.

Example: say you learn the card on Monday. Then your reviews look like this:

Day	Date	What you do
Day 0	Monday	Write the card. Read it aloud twice. Ten minutes later, cover it and write it again.
Day 1	Tuesday	Write all five numbers before you look at anything.
Day 3	Thursday	Same again. Also draw the air system from memory and say the L.A.B. check.
Day 7	Next Monday	Same again, then a timed Air Brakes practice test.

Each review takes five to ten minutes. Use this script every time: Cover. Say it. Write it. Check it. Circle the misses.

Write the question on the front of the card, like "The compressor stops at about ___ psi," and the number on the back. Never put the number on the front.

When you miss a number, repeat that review tomorrow

Here is the rule:

What happened	What to do
You got all five on day 1	Do the next review on day 3 as planned
You missed any number on a review	Repeat that review the next day, then go on with the schedule
Two numbers keep swapping	Study them as a pair: the pump stops high and starts again lower
You know the numbers but miss "what does this part do" questions	Go back to the parts drawing, not more number cards
You got everything on day 7	Move to timed practice tests and do one short number check the day before the real test

Try the leak trick, then check it in your manual

Some students use "123 / 234" for the leak checks: 1-2-3 for a single vehicle and 2-3-4 for a combination vehicle. Another version is to start with 2, add 1 for a combination vehicle, and add 1 if the brakes are applied. These tricks help you hold the pattern. Read the exact leakage limits in your state's manual before you rely on either one.

Four mistakes that cost you points

Swapping cut-in and cut-out. The test asks for these numbers exactly, so a swap is a lost question.
Learning the numbers once and never looking again. They fade before test day. The day 1, 3 and 7 reviews are the fix.
Memorizing numbers with no meaning. You then miss questions where the wording is close but not complete.
Using one website's numbers when your state shows a slightly different range. Your state manual wins.

If you want more on how the test covers this section, read CDL Air Brakes Test: What It Covers and the Numbers. For a full week of study around it, see How to Study for the CDL Air Brakes Test: 7-Day Plan.

Do this in the next ten minutes

Take an index card. Write the five numbers from the table, high to low. Read the line out loud twice. Cover the card and write the numbers again. Then put three reminders in your phone for tomorrow, three days from now and seven days from now.

Let the reminders run for you

That 1, 3 and 7 day pattern is also how the Mistake Fixer in FirstTry CDL works: it re-drills the questions you missed at 1, 3 and 7 days. The questions are exam-style and built from the official CDL manual, and the free diagnostic takes about 10 minutes with no account. It shows your predicted score and which topics are weak, so you know whether air brakes is where to start. Take the free diagnostic

Rules such as question counts and passing scores differ by state, so keep your state's CDL manual open while you study.