Six Sigma Logo and Symbol

The Six Sigma symbol is the number 6 written with the lowercase Greek letter sigma (σ). Sigma is the usual symbol for a population standard deviation — a measure of spread. “Six Sigma” is a quality goal: keep the process so tight, and so well centered, that even several standard deviations of variation still fall inside the specification.

This page explains that idea, then keeps the logo gallery and the other statistical symbols already used on the site.

The symbol is not a logo first. It is a statement about variation: σ is spread, and six is an ambitious number of those spreads inside the specification.

What 6 and σ are saying

In statistics, σ (sigma) is the population standard deviation. s or SD is often used for a sample. μ (mu) is the population mean, x̄ (x-bar) is a sample mean, and N is population size. Those symbols appear in the gallery below because they show up constantly in control charts, capability studies, and exam items.

A process at a “Six Sigma” quality level is one whose width and centering leave about six standard deviations between the mean and the nearest specification limit (before any convention about a mean shift). Two numbers get quoted, and they are not the same:

If a normal process is perfectly centered and the specs sit at ±6σ, the long-run defect rate is a few parts per billion.
The well-known 3.4 defects per million opportunities figure comes from a common Six Sigma convention that allows a 1.5σ shift of the mean over time. With that shift, the remaining distance to the spec is 4.5σ, which corresponds to about 3.4 DPMO. When an exam or a vendor mentions 3.4 DPMO, they are using that convention — not the zero-shift math.

None of this replaces a capability study. Symbols do not make a process capable; data and a stable process do. For process behavior over time, start with statistical process control charts and the core metrics.

Logos versus statistical symbols

The “6σ” mark used on belts, slides, and certificates is a brand-style emblem. There is no single official logo that every company must use. The gallery on this page shows color variants people have used, plus the DMAIC wheel, which is a method symbol rather than a statistical one. For mapping symbols used on process maps — terminators, decisions, inventory triangles — use commonly used Lean Six Sigma flowchart symbols.

Exam notes

You should be able to identify σ as standard deviation, μ as the mean, x̄ as a sample mean, and N as population size, and to explain what “Six Sigma quality” is aiming at. If a question cites 3.4 DPMO, look for the 1.5σ shift convention. If it asks about a centered normal process at ±6σ with no shift, the defect rate is much lower than 3.4 per million.

Lean Six Sigma Symbol

Six sigma symbol is a combination of the number 6 and the lower-case Greek letter σ which stands for standard deviation in statistics.This is a symbol of a quality improvement methodology which uses a variety of management tools (diagrams) and statistical analysis methods to remove defect causing variation from manufacturing and service delivery processes leading to increased customer satisfaction and profitability.

Six Sigma Symbol Gallery

Find various six sigma logos in this gallery ranging from green to multi color combinations.

Other Six Sigma Symbols

There are other symbols which are frequently used throughout lean six sigma projects. It is important to be familiar with these symbols not only for six sigma certification candidates pursuing self guided six sigma training but also for long time practitioners