The Shop-Floor Guide to DPPM vs. DPMO

In conversations about “Six Sigma level” performance, I hear people using DPPM and DPMO like they’re the same thing. And in fact, they’re close, but not interchangeable. Among manufacturing quality professionals though, this distinction matters critically when describing how good (or how bad) a process really is.

The Simple Breakdown

DPPM (Defective Parts Per Million) measures how many units are bad out of a million units produced. DPPM is commonly used in non-repairable components that are either good or bad. Think of fasteners, simple electronic components, and bearing balls. Each defective component is counted once in our DPPM calculations.

Example 1 – Simple Machining Operation

You’re running a turning operation on a shaft. The only characteristic you care about is diameter.

• Yesterday you ran 50,000 shafts.
• 25 of them were out of spec on diameter.

DPPM = 25 / 50,000 = 0.0005

0.0005 x 1,000,000 = 500 DPPM

Here, each part effectively has one opportunity to be “good” or “bad”. So DPPM gives you a clean, intuitive measure. It answers the question:

“Of all the parts we produced, how many were nonconforming?”

DPMO (Defects Per Million Opportunities) measures how many defects occur per million opportunities for a defect. This matters when one part can fail in multiple ways.

Example 2 – Printed Circuit Board Assembly

You build a board with 200 solder joints per board. Each solder joint is an “opportunity” for a defect (void, bridging, etc.)

Yesterday, you built 1,000 boards and found a total of 40 bad solder joints.

Opportunities = 1,000 boards × 200 joints = 200,000

DPMO = 40 / 200,000 = 0.0002

.0002 x 1,000,000 = 200 DPMO

Now compare that to DPPM: If those 40 bad joints occurred on 30 boards, then 30 boards were defective.

30 / 1,000 = 0.03

.03 x 1,000,000 = 30,000 DPPM

200 DPMO sounds excellent, but 30,000 DPPM sounds terrible. Yet they’re both correct because they’re answering different questions.

DPMO tells you: “How often do we mess up across all the possible ways this product can be messed up?”

DPPM tells you: “How many pieces are bad?”

Which One Should You Use?

Here’s the practical way to choose when to use DPPM:

• You’re talking about customer impact: how many bad parts might escape.
• You’re reporting at the unit level: “We shipped 2 bad parts in a million.”
• The product is simple or you’re only tracking one characteristic.

Decisions related to final outgoing quality, warranty risk, and simple processes tend to rely on DPPM.

Use DPMO when:

• The product or process has many opportunities for failure.
• You’re conducting a Six Sigma process improvement project.
• You need a fair comparison between processes of varying complexities.

Complex assemblies with many pins, welds, solder joints, features, dimensions, etc. are typical candidates for DPMO since it allows you to compare a harness with 50 crimps to one with 200 crimps. Or a PCB with 200 joints to one with 500. It levels the playing field for comparison.

One More Common Confusion

Six Sigma tables (the ones that map sigma levels to PPM) are fundamentally about defects, not necessarily defective parts. When you hear, “Six sigma equals 3.4 per million”, that’s 3.4 defects per million opportunities (DPMO) under the classic 1.5σ shift assumption.

If your part has only one critical opportunity, then 3.4 DPMO = 3.4 DPPM. But if it has 10 opportunities, 3.4 DPMO no longer means 3.4 bad parts.

So the next time someone asks, “Is that DPPM or DPMO?” here’s an easy answer:

“DPPM counts bad parts. DPMO counts all the ways a part can be bad”

Clear and concise.Ray Harkins is the General Manager of Lexington Technologies in Lexington, North Carolina. He earned his Master of Science from Rochester Institute of Technology and his Master of Business Administration from Youngstown State University. He also taught over 120,000 student quality-related skills such as Reliability Engineering Statistics, An Introduction to Reliability Engineering, Quality Engineering Statistics, An Introduction to Quality Engineering, Root Cause Analysis and the 8D Corrective Action Process, Process Capability Analysis, and Return on Investment Analysis for Manufacturing through the online learning platform, Udemy. He can be reached via LinkedIn at linkedin.com/in/ray-harkins or by email at the.mfg.acad@gmail.com.