X-bar R chart

control chart for subgroup means and ranges

UCL = X̿ + A2 · R̄, UCL_R = D4 · R̄

The classic variables control chart for subgroups of 2 to about 9 parts: the X-bar chart shows the subgroup means, the R chart the ranges. For larger subgroups the X-bar S chart with standard deviations is more efficient.

Calculate it

Process Capability & Control Charts: Cp, Cpk, Pp, Ppk, PPM and confidence intervals with X-bar/R, X-bar/S or I-MR charts and all 8 Nelson rules.

Related terms

• Rational subgroup: parts made under the same conditions
• d₂ constant: range to sigma conversion
• I-MR chart: individuals and moving range chart