📏 Upper Control Limit Calculator
Calculate the upper and lower control limits (UCL/LCL) for a process control chart based on the mean, standard deviation, and sigma level.
What are control limits?
Upper and lower control limits (UCL and LCL) are boundaries on a statistical process control chart that show the expected range of variation for a stable process. Points falling outside these limits typically signal a special cause worth investigating.
The formula
UCL = mean + k × standard deviation, and LCL = mean − k × standard deviation, where k is the chosen sigma level (3 is the standard convention for most Shewhart control charts, capturing about 99.7% of expected variation for a normally distributed process).
This calculator is for general quality-control education and planning; real control charts should be built from actual subgroup data using the appropriate chart type (X-bar, R, individuals, etc.).