Upper Control Limit (UCL) Calculator

Your details

Select the control chart type that matches your data. X-bar charts use measured values; attribute charts use counts or proportions.
Number of individual measurements in each subgroup (2-25).
Average of all subgroup means, the center line of the X-bar chart.
Mean of all subgroup ranges.
Upper Control Limit (UCL)Control limits ready
52.4234

3-sigma upper boundary; points above this signal an out-of-control process.

Center Line (CL)50
Lower Control Limit (LCL)47.5766
UCL (dispersion chart)8.8788
LCL (dispersion chart)0
Estimated process sigma1.8057
LCL47.5766
Center Line50
UCL52.4234

X-bar & R control limits calculated.

  • UCL = 52.4234, CL = 50.0000, LCL = 47.5766.
  • The total control band width is 4.8468.
  • Estimated within-subgroup process sigma is 1.8057. The 3-sigma limits capture 99.73% of common-cause variation.
  • Any point plotted outside these limits, or any non-random pattern inside them, signals a special cause that warrants investigation.

Next stepPlot your subgroup statistics against these limits. A single point outside UCL or LCL, eight consecutive points on one side of the center line, or a run of six points steadily increasing or decreasing all indicate a process shift.

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