The ASQ CQE Formula Cheat Sheet: Key Equations to Know
You do not memorize a formula sheet for an open-book exam, but you must know which equation to reach for. Here are the essential CQE formulas.
The CQE is an open-book exam, which changes how you should think about formulas. You are not being tested on whether you can recall an equation from memory—you can look it up. You are being tested on whether you recognize which equation a problem calls for and can apply it correctly before the clock runs out. This cheat sheet organizes the equations worth knowing cold.
I am John Lee of Alpha Training and Consulting. Use this as a map of the quantitative territory, then practice each formula until reaching for the right one is automatic.
Process capability
- Cp = (USL minus LSL) divided by six sigma—potential capability, centering ignored.
- Cpk = the minimum of (USL minus mean) over three sigma and (mean minus LSL) over three sigma.
- Pp and Ppk use the same forms but with the overall (long-term) standard deviation.
Control chart limits
- X-bar chart limits: the grand average plus or minus A2 times R-bar.
- R chart limits: D4 times R-bar (upper) and D3 times R-bar (lower).
- The constants A2, D3, and D4 come from standard tables based on subgroup size.
Basic statistics and probability
| Quantity | Meaning |
|---|---|
| Mean | The arithmetic average of the data. |
| Standard deviation | A measure of spread around the mean. |
| Binomial distribution | Probability of a count of defectives in a fixed sample. |
| Poisson distribution | Probability of a count of defects per unit of opportunity. |
| Normal distribution | The bell curve underlying capability and control charts. |
Reliability
- Failure rate (lambda) = number of failures divided by total operating time.
- MTBF = one divided by the failure rate during useful life.
- Reliability of series systems multiplies the reliabilities of each component.
- Reliability of parallel (redundant) systems is one minus the product of each unreliability.
Turn formulas into fluency
A formula you have used fifty times in practice is worth more than a hundred you have only read. Work problems with a non-programmable calculator, tab your reference binder so you can find equations fast, and time yourself. For a structured plan that builds this fluency, see our guide to studying for the CQE exam.
Frequently asked questions
Do I have to memorize formulas for the CQE?+
The CQE is open-book, so you can bring reference materials in a three-ring binder. The real skill is recognizing which formula a problem calls for and applying it correctly under time pressure—not reciting equations from memory.
Which formulas show up most often?+
Process capability indices, control chart limits, basic descriptive statistics, probability distributions, and reliability metrics are the most frequently applied. Sampling and hypothesis testing appear as well.
What kind of calculator can I use?+
Prometric allows a silent, non-programmable calculator. Practice with the same type you will bring so you are fluent with it on exam day.
Written by
John Lee
President, Alpha Training and Consulting
John Lee has more than 25 years of experience in quality engineering and has personally earned every ASQ certification, including the Certified Quality Engineer (CQE). A Shingo Award–winning author, he has helped thousands of engineers pass their ASQ exams on the first attempt with a 94% first-time pass rate.
Certifications: BSME, MBA, CMQ/OE, CQE, CRE, CQA, CQIA, CQI, CCT, CQPA, CQT, CHA, CBA, CSQE, CSQP, CCQM, CSSYB, CSSGB, CSSBB, CPGP, CMBB
Alpha Training and Consulting is an independent training provider and is not affiliated with, endorsed by, or sponsored by ASQ. "ASQ" and "Certified Quality Engineer (CQE)" are trademarks of the American Society for Quality. Exam policies, fees, and Body of Knowledge weightings are set by ASQ and can change—always confirm current details at asq.org.