Range Chart Calculations

Plotted statistic

Rangej = MAX (x1, x2,…, xn) - MIN (x1, x2,…, xn)

where x1, x2, … are the n observations in the subgroup j

Center Line

Average Range

UCL , LCL (Upper and Lower Control Limit)

where R-bar is the Average Range , d3 is a function of n, and σx is Process Sigma, which is calculated using the Subgroup Range .

Notes: Some authors prefer to write this calculation for statistical process charts as:

where D3 and D4 are a function of n.

Learn more about the SPC principles and tools for process improvement in Statistical Process Control Demystified (2011, McGraw-Hill) by Paul Keller, in his online SPC Concepts short course (only $39), or his online SPC certification course ($350) or online Green Belt certification course ($499).