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X-Bar & S Charts are Control Charts designed for tracking the average of large subgroups of continuous data. They consist of two separate charts;  “X-Bar” stands for the “Average” Chart which tracks the mean of sub-groups of 6 or more data points and “S” stands for the “Standard Deviation” Chart which calculates the standard deviation within each subgroup. These charts are useful for detecting shifts in the “center” or average with large subgroups.

A classic example an X-Bar & S Chart is to track the food order cycle time to deliver packages by sampling 10 orders per day.

For a better understanding of X-Bar & S Charts, check out our Black Belt Training & Certification Course!

Elisabeth Swan

Elisabeth is a Managing Partner at For over 25 years, she's helped leading organizations like Amazon, Charles Schwab and Starwood Hotels & Resorts build problem-solving muscles with Lean Six Sigma to achieve their goals.

Tracy O'Rourke

Tracy is a Managing Partner at She is also a Lean Six Sigma Green Belt Instructor at UC San Diego and teaches in San Diego State University’s Lean Enterprise Program. For almost 20 years, she has helped leading organizations like Washington State, Charles Schwab and GE build problem-solving muscles.